My husband got me one for Christmas last year, when I was just learning to knit.
Now I prefer hand knitting, unless I'm doing something with lots of tedious stockinette. (The USM only does stitch patterns with a right (knit) side and a wrong side by default; anything else and you'll have to use a crochet hook or latch tool to manually change the stitch.) Still, the USM is nice for last minute gifts and stuff -- I can crank out double sided, 6-foot scarves in about 2 hours.
I guess the biggest thing is just practice -- it took me a while to get the hang of it without dropping every other stitch... or even worse, missing an entire row and dropping my whole piece off!
Anyhoo, here are a couple of the better USM links I've found: