As mentioned before, I pretty much work in a one-developer shop. This is not an excuse!
When I started a fairly sizable project last year, I tried to start off right and set up CVS for source control, learned how to use NAnt to build my solution, did some playing with NUnit for tests and also set up NDoc to do my documentation.
A year and a half later I look back with regret that I ditched all of these in favor of...nothing. I was worried about the maintenance around my whole “build regime“ and it seemed like all my effort was adding nothing of value to the project. I deleted my NAnt build files, didn't keep up with the many NUnit upgrades and add-ins and have not got any documentation to show.
My project is getting bigger and bigger (of course!) and I hope I'm learning my lesson - that tools like I've mentioned keep things in check rather than add to the complexity in the long run. So now I'm leaning back towards NAnt, I've swapped to Subversion (which I've pretty much installed) for source control and I'm trying to find good bug/issue tracking software for when my app goes out “into the wild”.
To get me started I'm looking at a great article on 15 Seconds called “Using Open Source .NET Tools for Sophisticated Builds”, and also Jan Tielens' NAnt BuildFile Builder (via Girish).