For all of you who have struggled to change a tire, try this nifty little tool from Crank Brothers:
http://www.crankbrothers.com/speedlever.php
I recently took an emergency repair course (from a woman! Thank you Sondra Spencer!), and was introduced to the speed lever. I can now change a tire (or put on new tires!) in 18 minutes, compared to 90 minutes before. I don't go anywhere without it!
And just to add to the conversation, I just replaced the cheapie original tires to my Trek with Continental Ultra Gatorskin 23's...so far so good with the first 100 miles!