Wil Shipley on unit tests:

http://wilshipley.com/blog/2005/09/unit-testing-is-teh-suck-urr.html

I think what he's saying is unit tests don't add much if you are doing UI type development. It is hard to write unit tests for UIs (web or GUI), so if most of your code is UI code, don't bother.

However, if you are writing a library that will be used by a lot of coders, unit tests are probably indispensable. Otherwise, you would never be able to make even simple architecture or design changes (refactoring).

No difference? That's pretty impressive. I wish I was able to look at your process. Either your engineers are extremely smart and anal about their practicies or your domain is very simplistic (ta-da lists).

At my previous start up we had unit tests run on the entire system automatically after every check-in (with CruiseControl) and whenever someone broke a test suite, everybody got an email with name of the offender and diffs of his code against the trunk.

We also had a "beer rule" about violatros gettings drinks for everyone, to make the process a bit more exciting.

Facebook doesn't have an automated test suite. I wouldn't call that a simplistic app.

really?! I would be shocked if they dont have at least automated testing on their most critical systems. Whats the source of that info?

we asked Mark Zuckerberg at Startup School

I'd say try to plan for how much you will need to scale your code, and also how many others will be working on your code.

As your code gets larger, and as you start to have others working on it (who could break it), unit tests become more important. If you dont foresee either of these happening, then the time investment for tests may not be worth it..