This is rather odd. I've been using Urchin on one of my client sites for a while now, and it's been pretty good. As an experiment, I installed Google Analytics on the site last Thursday afternoon. The Google Analytics stats were a little buggy (something about not being able to "confirm" the presense of the tracking code) but they seemd to be pullling accurate numbers when I graphed them (similar to the ~20-25k visits a day that the site gets). But, when I went into Urchin to compare the results I was rather dismayed to see my traffic was not being counted at all! Except for a strange 150-odd people that somehow got tracked. So I killed Google Analytics on Monday, and Urchin instantly sprang back to life.

Anyway - there's clearly a problem with installing Google Analytics when you're already using Urchin, but I can't see any good reason why this should be the case... can you? I'm debating leaving Urchin on as-is, or killing it and going solely with Google Analytics, but I probably won't do anything until the bugs get worked out.