I started a thread on this, or a related, problem awhile back and there is some additional information there. See:

http://www.flyertalk.com/forum/showthread.php?t=558533

My reported problem was that GMAIL would work from my PC, but not from the Blackberry - same account. The upshot was several days emailing back and forth with T-Mobile and then Google, with the problem escalated through several Google layers, and then the conversation just stopped one day. At the same time my GMAIL suddenly started working from the BB again, and has worked ever since. The assumption is that something was stuck in the BB somewhere - a cookie, possibly - but we never actually did anything to fix it, it just fixed itself one day - maybe something expired. Proposed solutions included sending new service books and clearing my caches, neither of which did anything to solve the problem

I'm actually currently having a small problem with GMAIL on my work machine, but not at home. When I log in from work I'll get a blank screen and then my messages will display when I hit refresh (this is IE). This I can live with!