I use Google apps for my domains, because the reliability of Google has been unmatched so far.
I work at a school, and we have Google apps accounts for each of our students and faculty, because Google provides it free for education. We incorporated it with our central LDAP server, so the student's login works throughout our network. It really has worked out well for the 4 years we have had the service. It dramatically reduced local traffic on our network and load on our servers. And, considering that some of our servers are still the old XServes with G5s, that is a HUGE plus.