EDIT (6/27/05 2:00 PM): Blogger has finally addressed the "clear:both;" code issue. They posted this on the Blogger Status page:
Monday, June 27, 2005
The launch of Blogger Images required a bit of new code that is causing some users annoying layout problems. Before launch, the templates passed our tests but because of the open nature of Blogger templates, we weren't sure which kinds of template modifications were going to be affected. We're hammering out the solution now and we'll update our help site with some workarounds today.
Meanwhile, some possible workarounds have been posted on bloggerforums.com.