autotest or watchr doesn't help startup times -- I'm not sure why you mentioned that here.
I don't think the performance problems are affecting ALL applications - some people don't see any problems. I do think there is something wrong in Ruby or Rails that doesn't happen in all code paths.
I'm not sure why you think that. Unless you use spork or something that preloads the rails environment then forks it on every test run, autotest/watchr will boot the whole rails environment from scratch on each run.
You're right. I'm distracted by the reported 20-30 second environment load time for each test when it only takes about 7 seconds for my tests to start with autotest in my current pretty large app on an older MBP.
Autotest doesn't help startup times, but it can help mitigate the problem somewhat since the tests will start almost instantly when you change a file, saving a few seconds.
It's a good suggestion, but doesn't solve the problem.
I don't think the performance problems are affecting ALL applications - some people don't see any problems. I do think there is something wrong in Ruby or Rails that doesn't happen in all code paths.