My attitude as a consumer is caveat emptor. I read this article about GMail that outlines 4 major problems:
Problem 1: Gmail is nearly immortal
Problem 2: Google's policies do not apply
Problem 3: A massive potential for abuse
Problem 4: Inappropriate ad matching
In the section about inappropriate ad matching, the article mentioned a lawyer experimenting with Gmail: He sent himself a message, and discovered that the law practice footer he uses at the bottom of all of his email triggered an ad for a competing law firm.
This goes without saying. What did he expect? That's what Google Adsense does. To me, any professional using a web-based e-mail account is going to look unprofessional. Even eBay and other online retailers discourage webmail accounts. I see webmail more for personal use, and even then if there is anything truly confidential I would rather phone the person. Of course, the most cynical would start spewing about phone tapping, but I doubt there's anything in my life that would warrant interest in phone tapping... er, except for that one time... :)
On that note, I still have a bunch of GMail invites left, if anyone is interested. I keep giving 'em away, and Google keeps giving me more!