A ZDnet blog entry named GMail code hints at coming domain feature uncovers a theory that Gmail will eventually be available for any domain name. Meaning, I can set my rustybrick.com account to work on the Gmail Web platform. The article notes that Yahoo! allows this for a paid fee, but I have a feeling that Google, if they launch this, will give it away for free. This enables Gmail to capture a much larger user base, enabling them to learn more about the users and the domains, bring Web search to the next level.
I personally would not use Gmail, but some would. Take it to the forums.
Forum discussion at Search Engine Roundtable Forums.