Let me just add my experience with Google. It looks like the intermittent problem happens when you have multiple devices connecting to Gmail. Google seems to limit the number of devices/IP addresses connecting to the same account, at the same time.

Anyway, I have successfully synced my contacts (I don't care that much for email and calendar btw) to the N900 via MFE. If you encounter a timeout while syncing your Gmail account via MFE, quit and on the N900 browser, go to any of the following (I created them so I can easily go to them):

http://tr.im/gunlock
http://bit.ly/gunlock

I created the 'gunlock' tag/url (which stands for Google Unlock) on most URL shortening sites so try using others if you don't like tr.im or bit.ly.

Btw, this works on any device when you experience the problem connecting to your Gmail (e.g. iPhone, Palm Pre).

Hope this helps.