Scott Berkun has the most coherent, well thought out post on self publishing that I’ve seen in a while. It’s up at Should you self publish your first book?.
I’ve published 4 non-fiction books now with a publisher who specializes in technology books and I’ve self published a few small things. I’ve seen both sides and I think there are plusses and minuses to both. Much of may depend on your personality and what you want out of publishing.