Hej,
1. can't reproduce that "bug", chrome 5 and chrome 6 doesn't show that white box (tried it on my blog:
http://blog.splash.de/?s=youtube )... a link to your blog may help.
2. you can change that is your stylesheet (css).
3. not yet (it is on my todolist...), actually you only get a notice from wordpress that there is an update for floatbox plus...