At first glance, the online gossip community Oh No They Didn’t (ONTD) offers snarky commentary on people’s 15 minutes (or longer) of fame, from Jon and Kate’s marriage breakdown to Britney Spears’ tour lipsyncing.

Yet what differentiates ONTD (Best Gossip Blog winner at the 2008 Weblog Awards) from competitors, such as Perez Hilton‘s scrawls or Dlisted‘s sniping sarcasm, is the sheer power of its moderated user-generated content.

It has 90,000 members, more than 150 posts a day and scores of comments from readers (and I’m not even going to get into the numbers of ONTD’s popular weekly Free For All Friday postings).

Here’s a helpful guide for wading into this online community.

In the five years that ONTD has dominated online gossip culture (Perez Hilton has even been blamed for taking ONTD’s items), the community has broken a number of hot Hollywood stories. These include Jamie-Lynn Spears’ pregnancy and Fall Out Boy rocker Pete Wentz “Peengate” (the 2006 photo scandal where nude photos of Wentz made it onto ONTD).

As the ONTD community has grown beyond the confines of solely gossip content, “official” spin-off communities have been created to support users’ diverging interests. These include ontd_discussion (spoiler-laden TV and movie discussion) and ontd_political (check the hilariously modified CNN logo and mocking news ticker as its front page header).

Click onto the popular fansigns tag and be inundated with “Guess who I met?” postings with celebrities ranging from Taylor Swift to Tobias Fünke (Oops, I mean David Cross) snapped holding up a sign declaring their love for ONTD, which has helped to promote the community to the very celebs they often roast.

Of course, when ONTD users get up close and personal with a celeb, the fallout is intriguing. Back in September, Inglorious Basterds star Eli Roth tweeted about an ONTD posting discussing the film. But what innocently began with more Eli Roth tagged postings got a lil’ dirtier.

The star had a well-humoured reaction to discovering Inglorious Basterds gay fan fiction, suggestively taping a sign declaring his love of ONTD to his hairy chest.

It also led to the ire of a community when it turned out that a few ONTD members were sending private naked pics of themselves to Roth via MySpace.

His reaction? “I know this seems bizarre … but really for me the night was about tearing down those boundaries between celebrity and fan and the things we’re not supposed to say to each other.”