I love my GMail account, really I do, but I still keep copies of stuff locally. My IMAP spool is well over 5GB and still growing. GMail can't do that. Yet. Also, every once in a while, our Internet connection gets slow. Local e-mail is more predictable.

(Now, if Google offered a "GMail Appliance" that we could buy, and presumably give out whatever quotas we wanted, then I'd be twisting every arm I know in our IT department.)