I’ve just released an update to HTML Purified, a plugin that replaces the standard WordPress KSES filters with the much more powerful HTML Purifier library. This release tidies up a few rough edges and is jointly compatible with both WordPress and bbPress.
That’s right, the same plugin will work with both systems and allows you to fully protect yourself from any malignant comments that may be directed at your site. It should also ensure that your comments are valid XHTML.
Note that bbPress functionality is experimental. It works on the support forum here, running bbPress 1.0 alpha 6. Your mileage may of course vary.