For my primary email account I use FastMail instead of GMail. Why? FastMail is very fast, reliable, and feature rich. GMail is fast, reliable, and feature rich. I like the features of FastMail, but the primary reason I use it over GMail is the communication that they have with their user base when there is an (inevitable) problem. Here's a post about a recent problem:
This is the kind of thing I have never seen out of Google or Yahoo and probably never will. It's an advantage of being a relatively smaller service. They have maintained a policy of rapidly communicating with their user as well with a status blog in addition to their regular blog.
SalesForce implemented a similar "communicate with the users" policy after they had a major outage. You can see what they tell you about their service at http://trust.salesforce.com/trust/status/. Google Apps has a similar page at http://www.google.com/appsstatus#hl=en. Amazon has one as well: http://status.aws.amazon.com/.
Even small companies that are providing services in the cloud should have a status page and method for rapidly communicating with users when the service is down.
Historical note: back when I worked for CERL (Computer-Based Education Research Lab) at the University of Illinois I implemented a system variable on PLATO called zdegraded. It was used to allow programs (such as games) to modify their behavior (or become unavailable) if the system was running in a degraded state. The variable was removed within a year of being implemented, I suspect this was because the presence of such a system variable was viewed as poor public relations. This idea has changed now with the transparency competition on the web. Downtime is bad, but not having a way for your users to know what is going on is even worse.
P.S. I constantly evaluate whether I should stay with FastMail because GMail (and Yahoo as well) provide some nice to have additional services including calendaring. I use my BlackBerry as my primary calendar and synch with Outlook for that and address book management. I tried Google's sync, but was not happy with it at the time and was also tied in with Outlook for my day job. FastMail has some nice file management features and now that it has been purchased by Opera I'm less concerned about its survival longer term. I tend to review my email / calendar / address book situation every year though.