What is so wonderful about GMail is that everything is archived and searchable.
What is so not wonderful about the GMail-Salesforce mashup is that . . . it's not.
The GMail to Salesforce function is pretty useless. It only chronicles outgoing e-mail, if you remember to tell it to do so each and every time you send an e-mail or automatically if you initiate the e-mail from within Salesforce. But why would you initiate the e-mail from within Salesforce? GMail isn't integrated into e-mail so you'll naturally be in GMail for e-mail, not in Salesforce. Sure, if you do this chronicling, co-workers will have access to those outgoing e-mails, but CRMs like GoldMine have enabled the chronicling of both incoming AND outgoing e-mail for a decade.
Salesforce is the old topography. GMail, like the rest of Google, relies on tags not containers. Hence, unlimited searching, sorting, organizing. Hopefully this GMail-Salesforce mashup is just the beginning, but otherwise, at least in terms of e-mail, it's doa in mho.
The documents integration is much better, and I'll comment on that in a later post.