If you've used version 2 of the Calendar module, then you've probably been quite impressed with its fantastic Views 2 integration. If you're like me, then when you start using a new module, you often just enable all the little modules that comes along with it. In the Calendar module's case, this includes not only the main Calendar module, but also the "Calendar iCal" and "Calendar Popup" modules.
One quick tip that might help you save a little bit of time is to enable the "Calendar Popup" module only if you actually want it. I say this because once the module is enabled, the popups become the behavior of your calendars - there is no way to turn it off unless you disable the module. This fact escaped me for a few minutes before I bothered to read the documentation (actually, it was a comment in the documentation that provided the tip I needed).
There's a larger lesson here: don't enable modules just because you think you might need them. Be sure you know what you're enabling and why - it'll save you time in the future, I promise!