If you happen to use the LG CU500 (like me) and downloaded the latest Google Maps for Mobile (the one with the magic location stuff) - it doesn't work. Here's a thread about the problem on my LG and other similar phones. It pops up a message that says "invalid class" and then dies.
Upgrading just now to 2.0.1 didn't help the problem, so until they get around to fixing it, you have to downgrade by going to http://www.google.com/gmm/support.html on your phone.
I've gotten pretty used to having it with me, I have to say, and missed it this weekend!