Dashboard is really helping with the way I use my computer overall, especially iCal and Address Book. I suspect it's those two that make it hardest to switch from MS-E. For me, I use the iCal Events widget to display events for the next couple days. I have another instance of the widget that tracks my "finances" group where I keep my bills' due dates and paydays scheduled. I use the Address Book widget for quick lookups of information that's not accessible through another app, i.e. I only use Mail to look up email addresses because that usually means I am about to use it to send an email. Address Book usually stays open though because Salling Clicker uses it for Caller ID purposes.

If you use Salling Clicker, you can have Address Book log your phone calls and SMS and there is a script for SC that allows you to chart your phone calls as events on iCal. I couldn't trust this for keeping track of contacts though because it didn't account for calls/SMS when I had my Powerbook closed.

Finally, realizing I can sync my contexts to iCal is helping a ton! Like Merlin, I now live in iCal and plan in kGTD. I would like to see a widget that lets you view Tasks by Calendar group, with a drop-down box to switch between groups. That would make switching contexts a lot easier for me.