i did for 2 months with spotify just so i didn't have to deal with the ads. i prefer the way their mobile app looks compared to their desktop/web.
i have a premium account with spotify (and have had it since they launched in the US)
A lot of people always talk how much better rdio is and how bad spotify's UI/UX is, but it always seems to be about the free membership.
Personally i think spotify is pretty good and haven't really had issues (other than a few albums not being available)