What do you like best about the product?
UserTesting makes usability testing easy, and the results are fast. I usually run tests with about 5 users and will have completed studies in just a couple of hours, depending on the type of users that I'm looking for. One of the best parts is that for basic usability testing, you can use their panel and set up screener questions, which takes care of recruiting. This allows you to easily do a dry run and iron out any issues with your test script before launching it to other testers.
What do you dislike about the product?
The quality of testers is hit or miss - sometimes they're really good, and sometimes they're not. I've sent a few back for not reading the test instructions. However, the UserTesting support team is very responsive when you run into problems.
Recommendations to others considering the product:
It seems like the competition for these types of tools is intensifying. Overall, I've been satisfied with the tool, but I'd do a little research before deciding on one.
What problems is the product solving and how is that benefiting you?
I typically run remote, unmoderated tests for usability studies. I've tested all different fidelities from bare-bones wireframes to high-fidelity prototypes and live websites.