I'm putting the finishing touches on an update of the Plogger beta 3 Lucid theme, called Diffuser. It looks very similar, but the code as been substantially rewritten. It validates as XHTML 1.0 Strict, if you use the included modified core files that have been tweaked for just that purpose.
I've gone over everything pretty thoroughly in Firefox 2.0 and IE7, and it looks substantially the same in both. If anyone out there is using Lucid from the beta 3 download and having weird things happen with the layout, this might solve your problems.
I'm open to suggestions and if you notice anything buggy, just point it out here or at the download page and I'll happily patch it up.