In pride of place on the window-sill at Mumsnet's North London offices is an empty tube of 10 Downing Street chocolate chip biscuits, accompanied by a handwritten note in Gordon Brown's much-maligned script.
"To Carrie and Justine and the Mumsnet staff. My thanks - and the biscuits I enjoy," the Prime Minister has written, before signing off: "With best wishes, Gordon."
The unusual gift is a nod to "Biscuitgate" - last October's storm in a teacup when the PM was ridiculed for not being able to name his favourite biscuit in a webchat with the parenting group. Clearly, Mumsnet is no ordinary online network: since the site launched ten years ago, its community of "opinion-formers and early adopters" has started to inform the national debate, with the May election renamed "the Mumsnet election".
The affluent, tweeting Mumsnetters have also caught the eye of the media industry, thanks to their habit of banning ads that displease them - such as the Madeleine McCann cinema ad in Shrek - their high spending-power, their role as the family decision-makers, and their ability to make or break brands via word-of-mouth.
As we speak, Ford is working with ten members of Mumsnet to test the design of its Galaxy and S-Max models, and when some dimwitted viral marketers infiltrated the community with fake forum postings promoting Haliborange multivitamins, Mumsnetters reacted with fury, orchestrating a campaign that made "Haliborange kills otters" reach the top of the Google search rankings for "Haliborange".
But the advertising campaign that really made the group see red was ad agency Beta's outdoor campaign for the OAA, which was swiftly taken down from billboards nationwide after Mumsnet organised a mass protest (more on that later). As Beta's Garry Lace learnt to his cost when angry mums threatened to dump dirty nappies outside his office, the message is clear: don't mess with Mumsnet.
Roberts, a softly spoken but steely working mother of four, does little to dispel the hardline myth by describing how she has spent the day with the Today programme's John Humphrys. The presenter came to Mumsnet Towers to conduct a live webchat as research for a Channel 4 documentary on education and social mobility, and Roberts is still buzzing about the 500 "thoughtful and personal" posts left by members on the Mumsnet Talk forum. "He was charming; we could have chatted for ages."
Roberts, a former sports journalist for the Times and the Telegraph, has run Mumsnet full-time for the last five years. The site aims to make parents' lives easier "by pooling knowledge, resource and support", and has grown since its launch in 2000 to attract 1.2 million unique users a month and 20,000 daily forum posts.
Mumsnetters are typically 25 to 45-year-old AB women (although 5% are now dads), 75% are educated to degree level or equivalent, and they have an average household income of £56k. About two-thirds of the community work, of which half are part-time, and the site's 20 million monthly page impressions have made Mumsnet a magnet for baby and pregnancy, household and style and beauty advertising.
But although the site has made a pre-tax profit for the last three years, Roberts claims she is more interested in growing the community than making lots of money out of the business. And, in keeping with its members' strong principles, Mumsnet does not accept ads from Nestle or McDonalds, or for formula milk or cosmetic surgery.
Roberts, who has just banned an "all-singing, all-dancing" CBeebies ad from the BBC, says: "We turn away as much advertising as we take. We have never taken formula milk ads, which is a large spend in our market, and we have always turned away intrusive formats. We have to remain authentic and real; our credibility is everything."
Mumsnet describes itself as a community, not a lobby group, and Roberts insists the site has "no axe to grind". But she adds that she is "militant about parents' right to choose", and is currently working on a "Let Girls be Girls" campaign to challenge retailers selling inappropriate clothing to pre-teenage girls. "We don't have an annual agenda, but when there is coherence and cohesion about things our members feel strongly about, then we at HQ will facilitate that as much as we can."
In the case of Beta's ill-judged "Career women make bad mothers" ads in the New Year, Mumsnet members organised a mass protest through discussion on the site, writing to the ASA, the OAA and Beta's clients, and the offending creatives were promptly replaced.
When Mumsnet was threatened with legal action from lawyers acting on behalf of Beta founder Garry Lace, Mumsnet removed any defamatory forum posts, and the case was closed. Roberts draws a line under the episode with: "The irony was that Beta wanted to provoke a discussion, but not a free discussion."
Until the next storm in a teacup brews, Mumsnetters are busy tweeting, having fun manipulating David Cameron's face at www.mydavidcameron.com and then talking about their handiwork on Mumsnet, and quietly influencing brands' behaviour. Video diaries of the 10 members testing the Ford cars donated by the car manufacturer will be posted on Mumsnet, with a feedback thread where all can comment.
Roberts says: "Ford is the first car brand to interact with Mumsnet and this is significant. We have been saying for years that once you get to a family of four plus, it is the mum who does the driving around. It is not about engine size; it is about whether you can accommodate a car seat and fit the shopping in."
On 2 March, Mumsnet's many supporters are invited to the site's tenth birthday party at the Google multiplex in Victoria, which the search giant has donated as a venue for free, in recognition of Mumsnet's power in the age of social media. "[Google] recognises the fact that Mumsnet is a community that is helpful," Roberts says.
Johnnie Boden, founder of Middle England clothing brand Boden, is apparently keen to join the celebrations, and Gordon and David will no doubt make an appearance, election campaigns permitting. But will Garry Lace be on the guest list?
Roberts laughs. "I don't think Garry Lace would want to come."
Twitter is fantastic. We have received our fair share of legal communications [Mumsnet famously settled out-of-court with parenting guru Gina Ford] but let's just say if Twitter had been around, that case would not have got to court.
The Apple iPad
What's not to like about the iPad apart from the price? Apple should send us some to product test straight away. They are perfect for our networking, mobile, busy mums.
The Mumsnet election
Women are a key vote in this election. Traditional Labour voters are toying with Cameron, and they may make the swing. We have noticed a lot of discussion along the lines of "I have never voted Tory before but I am considering it - or should I?" We are not reflective of the population at large - we are quite liberal leaning - but the important thing is that many of our members are undecided.
Politicians using social media
For the first time, politicians are trying to use social media in their election campaigns: it is as important to them as traditional media. Using Mumsnet is an attempt to be seen to be using social media in a non-embarrassing way. And politicians enjoy speaking directly to people. Gordon Brown told me he likes talking to people without the media getting involved because he is so often spun against.