On my servers, I use google apps for domain/gmail to handle the mails. Why ? because I tend to move from different hosting times to times (Like before having my own server, I was at dreamhost), that's why I like to use the gmail infrastructure to handle my mails as it is working pretty well. (+ I have all the gmails features, and one of the best antispam in the world).
I would really like to have google.com/a integrated as a mail option in virtualmin: -If my domain is set to use this, the dns records a set accordingly (spf + mx + cname like mail.domain.com) -Maybe it would be possible to configure mailman to use one of my gmail accounts -etc etc.
I think that would be a cool stuff.