The build for our main site was taking nearly 8 minutes on the CI server, getting dangerously close to the recommended 10-minute limit. And I'm talking about the basic, commit build. However, a "nant all" on my machine took about 2 minutes! WTF?!? Then I remembered that I installed CruiseControl on a crappy old 512mb RAM machine!
I moved it to a newer, faster server, and problem solved :-)