I'm sure this is a bug in 3.0.5 because I noticed it on a new site that I created some days ago. It was a new installation from my hosting control panel but it still needed updating to 3.0.5. I noticed the entire page was being pushed down about 30px and have not fixed it since.
Here is the strange part. When viewing the site on another domain i.e. my main one is .com but I tried .eu. It looks fine! I refreshed and visited multiple times to find it was the same.
Why would WordPress display differently based on the domain? You would think it is a CSS issue, but the gap appears when viewing on the normal domain, the one that would show in all the paths to style sheets.
I've just updated my main site to 3.0.5 and suddenly noticed the problem there. No plugins have been changed or anything, just the update to 3.0.5.
It's making my site look crap.