Best way to organize to-dos in iCal, Mail, .Mac

All this time I've been organizing my iCal and Mail to-dos using calendars I already had in iCal before Mail gaining the ability to handle to-dos. These older calendars are e-mail address independent and show up in the On My Mac section in Mail's To-Do box.

Now with the new MobileMe features coming, I'm wondering if I should migrate those over to my .Mac email address instead of just having them show up in the On My Mac section in Mail's To-Do box.

I'm about to get a new Mac and so now is an ideal time to change these over.

Thanks for any advice or suggestions!