Don't have a surefire resolution for you, but I can share my setup that has been working fine.
1) My google account is my "gmail.com" email. I also used to have a different non-gmail logon to google, but switched to the "gmail.com" logon a couple of years ago.
2) I have a Sprint 1.4.5 Pre-
3) I have the launch-day Touchpad
4) I use google to handle my calendar and my contacts (and a small amount of gmail) to both my TP and my Pre-. I also sync my work's Outlook calendar to google's calendar via their "google calendar sync" windows program.
It has been working flawlessly for me. My calendar, gmail, and contacts sync great (both ways). Some have reported that the calendar only syncs a few months forward/back, but honestly I'm looking at my Touchpad calendar has one-time and recurring events going into next year, so all of that seems to be working fine for me.