Just read a rant that unit tests are all but worthless. Is this true? Let's start at the beginning. Unit tests are supposed to validate independent pieces. They attack at the function level. Code with many dependencies do not work well with unit tests.
Unit tests may help find some small errors. However isn't that what debugging is for? I am speaking hypothetically here. You are supposed to be able to refactor your code and run your unit tests to check whether it still works. Unfortunately unit tests may be too brittle to still work after refactoring.
Developers are optimists. Therefore their unit tests may just choose the easy cases. That is not much of a return on investment. However you should use a tool like Jester. It rewrites your Java code to tweak the logic a bit. If you Jester your code, and the unit tests still past, your tests are not doing much.
Acceptance tests are better predictors of whether your code works. These can be employed after a refactoring to make sure the code still works. Some people still swear by unit tests. They have stories of doing 100% coverage. Then the eventual deployment had no problems at all. I think the jury is still out on unit test effectiveness.
A Little Bit of Crypto - I have been trying to figure out to "collision resistant" some of these standard hash functions are. It is a tough concept to get my head around. I figure...