Having thought for a while about which way to go with filtering tags (only allowing certain ones, or only denying certain ones), I'm going to put my support with denying certain tags. Allowing only certain tags then limits our ability to include special characters:
, &, etc
and that also means that when things move more towards XHTML, the filter needs to be extended or rewritten.
I think it's easier to filter out the bad/naughty HTML then to make a special case for all of the different HTML features we individually use...