Google offering Gmail for domains
A few days ago, Google announced their plans to offer Gmail services to corporations. They are presently testing a beta of the service which allows you to customize Gmail to make it look as an integral part of your organization. I guess this could be the perfect solution for SMBs who do not want to have the hassle of setting up a mail server and hosting it locally.
"This special beta test lets you give Gmail, Google's webmail service, to every user at your domain. Gmail for your domain is hosted by Google, so there's no hardware or software for you to install or maintain."