I have read a really good article at
http://blog.wekeroad.com/blog/my-enemy-my-self/
I is really interesting, and indicated lots of thoughts in me, I think the unittesting is an essential and a must have in every software project, but the way you implement it DOES matter. I am developing a little framework and started it without unittests, after I have written all the unittests to the top level classes, it helped a lot. When something went wrong at the lower level of hierarchy I was able to debug it and find solutions for the upcoming problems in an easy way. It came I started to write the unittest of te low level classes, and started a bigger refactoring as well, it took a long time, much longer if I haw written all the unittests at first, BUT the problem is if you write unittest too soon may tend to start the "refactoring" too soon and has no results, just tests that doesn't satisfy your customers.

It looks simple to write good and practical unittesting, but it takes time to have the skills and a good and healthy view on it.