Harry Brignull did a thorough review of WhatUsersDo.com, a UK-based remote, unmoderated, qualitative usability testing service. To use the service, you pay £25-£30 per participant and you get back screen recordings with audio of them thinking aloud during the tasks. The test participants are chosen from a pool of users paid to take usability tests, similar to usertesting.com.

As Brignull notes, this is possibly valuable to companies with little experience doing usability testing on their own before, but is less likely to be of value to companies with the experience and budget for doing moderated usability research on their own, or with a usability research consultancy.