Even if CheckUser were used, surely any user with half a brain would be using a VPN or be behind manual proxies?
If you want see how CheckUser works, sign up for a test wiki where they let people play with mod tools or install your own instance of MediaWiki and try it out.
Having done so myself, the above is usually true. CheckUser is nigh useless on anyone using a proxy almost all the time, though somewhat more effective for Tor nodes, since those can be tracked as Tor nodes (TorBlock is even better). CheckUser can be paired with honeypot IP checkers, spam hunter sites, and other online databases to weed out common spammer IPs and commonly known internet dickheads, but it's by no means an end-all, be all cure for sockpuppeters. IP blocklists, restricting certain editing privileges, and instituting things like the VandalBrake RationalWiki has can piss off sockpuppets much more easily.