I want a group of random people with random browser and OS specs to use my website and report bugs. Is there a service like this, where you get standard reports with technical specs of the users and qualitative feedback as well?
Realistically, if you're looking for tech compatibility, you may need to do it yourself. It's not as bad as it seems, but you do have to test 3-6 browsers/OS combos. If you've used good stuff like jQuery, etc., lots of the browser differences can be made minimal.
Also, you're probably not going to get particularly phenomenal feedback from just any user. Try doing the testing in person, with just a few people (Jakob Nielsen has a post about how many people you need, and concludes something like 3 people will give you the majority of what you need to focus on. After all, you want to focus on the big issues, and as a startup you're likely to have tight resources available...)