WordPress 2.5 introduce a new automatic upgrade feature for plugins. This works fine for the most plugins and users, but there are some behaviour which you should be aware :
- Additional files in the plugin folder will be deleted : When you start the upgrade, WordPress delete the existing folder with all the content. If you have created additional files into the plugin folder ( i.e. custom style files, language files) then you must reupload them again.
- Binary files sometimes not working : After 5 bugfix releases for NextGEN Gallery, there are still a problem that after the upgrade the sildeshow or language file are not working. There is some unknown failure, which could be some permission issue. If you encounter such a failure, please reupload all files manually per FTP.
Good luck !