I have committed new experimental option for cleaning of untrusted html text with HTML Purifier into HEAD. See Miscellaneous/Experimental section in admin tree menu.
Benefits:
* believed to be more secure
* produces valid xhtml code - no more unclosed tables breaking page layout
* converts obsoleted tags to new alternatives
* actively developed
Regressions:
* slower
* does not support MathML tags
You can find more info about HTML Purifier at http://hp.jpsband.org/
Please report any related problems into the tracker
skodak