A UGC (User Generated Content) site is as good as its C.
While we provide the tagging, categorization features, but users may not abide by that, hence search may end up bringing irrelevant result. Like I can think of 'report spam' link, up/down-grade. What are some of the other basic methods of maintaining the sanity of data? (our site has title, description, tags, categorization - think youtube).
Bozo filter. When you ban someone for posting crap, don't delete their crap, just flag it and only display it to that user. By giving the crap posters less feedback you reduce their ability to evolve new crap-posting abilities.<p>On the reverse side, you must also identify your best posters. It's easy to forget while dealing with the obvious problems with crap, but you must find the content that is highest-rated, that draws the most traffic, that most contributes to your business goals. Praise them in public. Send them swag. Make sure your customer service system highlights them, so you're responsive when they have problems. The best users are around 100x more valuable than average. Identify and cultivate them.
I'm assuming free-form textual data here, if you're doing something more constrained (like CDDB data) this will probably not be helpful.<p>You can push the problem around with technical features, but I believe this is a meat-space issue and needs to be treated as such.<p>Hacker News (so far) is one of the best run sites I've seen in this regard. My belief is that the community is focused on a small enough segment of content that it doesn't bring in contrarian intellect points (i.e. OMG LOLCAT, political bickering black holes). Explicitly defining a charter for the site -- giving users a target to moderate to -- is probably the single best thing I can think of.
User moderation is very useful, as are editors. Filtering NSFW content by tagging it and requiring users opt-in to see it makes sense. There are also copyright issues that are important. You want to make it easy and fast to identify copied material and yank it, in case of a DMCA takedown notice.<p>You could also let users tip content, and get the data from tipjoy as another ranking tool. Email me ivan@tipjoy.com for more info.
automate it, suspend posts that gets tagged a lot with "spam!" then give the original poster ability to dispute. It'll cut down the effort on your part big time, since spammers most likely won't bother appealing