I have had some battery drain issues since I received my N1 3 days ago. I found that Android 2.1 has a nice battery log (/d/battery_log) which updates every 50 - 55 seconds. In doing some tests to see what was killing my battery I can tell you that it isn't WiFi.
I would say that when in use, 3G draws a bit more than WiFi when actively used, but when WiFi is just idle it seems better than when 3G is connected and not in use.
In case anyone cares...I am still isolating all of the battery drain issues, but one of the biggest I have eliminated by uninstalling seems to be from BeautifulWidgets. I found it hard to believe, but my testing seems pretty clear. I also have a decent draw whenever I'm in the car with Bluetooth sync going. I would have had a hard time confirming this without this battery log file.