Great article about the power of mturk. If you aren’t wanting to deal with the intricacies of mturk, there is a service called PickFu that is built on top of mturk that can give you similar results for simple A/B tests.
Another tool built on top of mturk for doing remote user testing is UserBob. The UserBob service will get users to record a video of themselves using a website or app for the first time while they talk about the experience. [disclosure: I built UserBob]