Similar trick with contacts, which I never bothered with until I had an Android phone and it became mandatory. I went through a bit of pain, once, to get my contacts out of Apple Address Book and loaded into Google. I then spent a solid afternoon merging duplicates and cleaning up the mess. Now, I have all my contacts in Google, seamlessly showing up in my Android phone. Similarly, all my calendar stuff lives in Google and shows up nicely in iCal.

Now that it's done, I never touch Apple's Address Book any more and I rarely touch iCal. I mostly just use the Google web site.