I've noticed that all sync applications (Marketplace, mail, Facebook) will stop working after about 10 minutes from reboot. If I reboot (and make no changes to any of my settings), I can sync my Google Mail (and other accounts) as well as download Marketplace apps. However, after a few (10) minutes, my phone no longer can download apps in Marketplace or sync (eg: the Error code: 80072F78 when trying to sync Gmail). Under the email+account Settings, I'll see "Not Up To Date" for the various accounts.
I can, however, access the internet through the web browser. I can also view and search for apps (but not download) in the Marketplace.
Note that I noticed that one reboot over the last 3 didn't result in the temporary fix but after rebooting again, I was able to sync temporarily.
Anyone experience this?