Board Thread:General Discussion/@comment-5797509-20140902002109/@comment-4568327-20140902011328

CheckUser is not to be taken lightly. On Wikipedia, CheckUser is used to rat out sockpuppets and to locate the sockpuppets of vandals. A CheckUser there found to be looking up IPs "Because I was curious" get the tool removed. CheckUsers should generally be 18 and older and have a strong history of contributions. When a user performs a CheckUser, their operation is recorded in a private log that only other CheckUsers can see. If a CheckUser is locating a sockpuppet, they generally only give out their results like "User A may or may not be the same as User B", never posting the actual IP address. Also keep in mind that there is a lot of information that CheckUser can't provide. You still can't determine whether the user was actually deciding to mess with the wiki or if their little brother got on to their user account (which was so not password protected).

So, in short, for 99.99% of cases, use Special:Contact/general to request a CheckUser, but an operation will only be performed if there is a good reason for it. "Curiosity" is not enough.