A few people have mentioned that they are having issues with GPS after updating to 2.0.1 - here is a temporary fix until 2.0.2 comes out:
1) Disable 3G
2) Turn your iPhone off and on again
3) Turn it back on again
4) Open up Maps and hit the button
5) Turn 3G back on again
I'm not sure if this will need to be done every time (I haven't had a chance to extensively test) and I'm not 100% sure on why it works but it does; but until 2.0.2 comes out to fix this issue (it worked fine in 2.0.0) I thought this might be a useful tip
1) Disable 3G
2) Turn your iPhone off and on again
3) Turn it back on again
4) Open up Maps and hit the button
5) Turn 3G back on again
I'm not sure if this will need to be done every time (I haven't had a chance to extensively test) and I'm not 100% sure on why it works but it does; but until 2.0.2 comes out to fix this issue (it worked fine in 2.0.0) I thought this might be a useful tip