I've been using Gmail now for a little bit and it works pretty well -- I'm impressed with the Gmail interface. There are still some things I need to experiment with like attachments and keyboard shortcuts (are there any?) but right now, I'm not feeling much pain after using Gmail for a while. I wonder if there will be pain associated with not having my calendar or tasks in Gmail.
One thing that I wish worked better: I've setup my personal and work e-mail addresess to both forward to my gmail account and I've also verified both against my Gmail account so I can send e-mails from personal/work addresses from with gmail. But one problem I've encountered is that Gmail doesn't make any inferences about which e-mail address to use when replying to a message -- it simply uses whichever e-mail address you've marked as default. In my case, I have my personal address marked as the default so when replying to work e-mails, I have to CLICK on other choices (under the from address) and then I have to CLICK and CHOOSE my work e-mail address. Three extra clicks, in my opinion. Hey Gmail product people: why not do away with those extra clicks?