I like to use assert a lot. I find it very useful when I am building applications for the first time (perhaps for a new domain). Instead of doing very fancy error checking (that I would consider premature optimization) I code fast and I add a lot of asserts. After I know more about how things work I do a rewrite and remove some of the asserts and change them for better error handling.
Because of asserts I spend a lot of less time coding/debugging programs.
I've also noticed that the asserts help me think of many things that could break my programs.
