I have found an annoying bug in the ActiveDirectoryRoleProvider, or acctually not a bug so much as an ignorance for not so talented AD creators.
When the GetRolesForUser() method is called the provider does a recursive method call for all roles, the problem with this is when the recursive call finds a group that is member of a group that also is member of the previous group, this creates an eternal loop until the application pool crashes.I would have hoped this would have been fixed in the R2 release where the roleprovider is compiled into the assembly but that wasn't the case.

Didn't find anywhere to report a bug without starting an very long support process so I put it here so people are aware of this issue and hopefully EPiServer will fix this sometime soon.