I get a 502 server error.

http://groups.google.com

no problem here
and BTW I'm on groups.google.FR for 1 hour and I didn't have any problem.

It was very slow for me and eventually loaded but without any stylesheets. The home page seems fine now but loading a particular group isn't working for me right now.

It loads now, but the problems seems to be common:
http://groups.google.com/group/Gmail-Help-issues-logging-in/browse_thread/thread/82ef0293f6d5d0e2/31c29de8aaf57630#31c29de8aaf57630

been there all day, havent notice a thing

using a european IP, so I guess i'm on european cluster.