Hiya,
I'm suprised no-one else has reported this problem, you are the first! I discovered this problem over the weekend. When I open the Gallery application it just sits there and says "Loading...". The photos never come up.
Not sure that this is a problem specific to the Galaxy S 2 as my mate has the Nexus One and it suffers the same issue. He thinks it is intermittent and that if you close the app and back up again it should come up ok. I tried this but it didn't work for me.
I thought maybe it was an issue with my SD card (where the photos/videos are stored) but I used ASTRO (file explorer app) to view the photos no problem. So not sure what this is, maybe a 2.3 problem with Android as I never saw this on 2.2.
Keep me posted with how you get on...