I'm in the process of seeing how much breaks when using jUpgrade to go from J1.5.25 to 2.5 (almost everything) on a test clone of my site. Re-installing CB 1.8 (it didn't pick up my CB1.8 install on the upgrade) got my lists back and users to show, and their avatars show up. All connections also seem to show up. I'm slowly going through the process of upgrading all the CB plugings/addons if they need it.
I'm not getting errors (well, I can't have the debug system on because it breaks the site), but none of the user uploaded Gallery images show up. I know they're in there somewhere, I'm just not sure what I should change to get them to show. The gallery tab is there, it just says there are no images in the person's gallery (when they do have them on the functional 1.5 site).
Edit: This is for CB Profile Gallery RC1.2, which I believe is the latest.