I'll be very surprised if I'm the first to post on this minor if troublesome issue, but since it continues to pester me, I figured I might as well sound off with what's worked for me as a solution.
What I've found with the upgrade to 2.6.3 is that my images won't display aligned to the right. They look that way in edit mode, but never in the actual post (at least not on Firefox 3.0.3 on my Mac).
So I took a look at the code and the problem appears to be in the img tag:
The class="alignright portion didn't look right so I took out the class=" and changed it to read: align="right" so that it now looks like this:
And voila, my photos are now back on the right where I want them to be.
Just passing it along in hopes if you're suffering from this syndrome it can help you too.