I did some testing, but not much when I worked for a startup.
If one bad programmer writes the unit tests, and another bad programmer writes the code, then you might end up with a mediocre outcome, instead of a bad outcome. Same with pair programming.
Likewise, if you get a good programmer to write the unit tests, then give the programming work to a terrible programmer, given enough time, he'll write a working solution.
But TDD benefits even the best programmers when they are dealing with a huge, ugly, old code base.
When on the other hand you're user testing every day or multiple times a day, like you might with a web startup, then TDD may only slow you down.
These days I'm at a point where I can usually push 4 or 5 new releases into production every day. It's pretty awesome :-)
But I can see how right now it seems their time is better spent on other things.