I tried switching my googlemail account to gmail over the weekend. At the moment I would NOT recommend this to anyone on an Android phone.
After switching the account on the google website, the functionality of the phone was heavily compromised. To start with, updates from applications in the Market Place just hung and never actually started. I also had problems syncing google contacts.
I reverted to the googlemail address again and things appear OK. Had a look around this morning and clearly this has been known for a few days:
http://www.google.com/support/forum/p/Talk/thread?tid=6083ec77fd817408&hl=en
At the moment doesn’t look like there is a fix apart from reverting the address domain.
UPDATE
Hmm – my primary calandar was not coming up/syncing. It disappeared from the Handset calendar but was clearly available on the google calendar.
Followed the instructions here
http://www.google.co.uk/support/forum/p/android/thread?tid=1fbb1eb21f4ebc02&hl=en
i.e.: “From the home screen hit menu, then settings, then applications, then manage applications, menu, filter to all
Now you should be able to locate ‘Calendar Storage’ tap it, then tap the clear data button.
Now reboot and all will be well.”
That worked for me. Calendars now back without having to perform a factory reset (which some other threads have recommended).