Since TYPO3 6.0 the backend module user admin has been rewritten. I used this tool to check which users are in which usergroup using the compare checkbox »Member of groups«. Now this option is not available anymore and there is no other option to check wich users are in which usergroup (except looking in every user record).
Updated by Bernhard Eckl about 11 years ago
The first one (Which groups a user has) is it, it was in the previous T3 versions. But the second one also sounds very useful. Actually I don’t know how to manage this if there are a lot of users and groups.
There is also an extension called tc_beuser maybe it’s an inspiration for this.