I know that NextGEN is supported up to WP 2.7 but I'd like to share this as this may help to prepare an important upgrade in the future.
I've installed NextGEN (the newest version) under WP 2.8 Beta 2.
Everything works just fine except one thing:
if you try to add a gallery to an album, the album doesn't save settings resulting the gallery is not added at all.
In other words if I create an album, I can't add any galleries there. I drag them to the album area and drop it there. If I try tu update these changes, they can't be saved.
All other functions seem to work fine.