For me, I think from within people menu I copied contacts and an option appeared phone/sim/google. I selected google and away it went. I didnt have my contacts setup to automatically sync to gmail, I had to do it specifically.
Regarding the apps, when I reset my phone in the past after entering gmail settings on the reset phone, I went to market and it had a list of all the apps I had previously installed/bought and I just selected which ones I wanted to reinstall. - was surprised that some of the app data was reinstalled too. Not sure how I feel about that as it suggest that google has my app data files too.
Currently I am using an HTC hero until the One X is fixed. When I added my gmail login to this phone when I went to the apps store it just listed the (fewer) apps that are compatible with this older phone.