Like it or not (and there are a lot of people that are both sides of the issue), Google has released a suite of its products that will work on your domain. Here’s where I net out on the issue:
I like Gmail and use it a lot. If I had a domain behind which was a small business, and I wanted a very user-friendly e-mail program that all my employees could easily access, I’d probably go with the Google suite at this point in time. The Google Calendar portion is nice, but still a little lacking in features; chances are that it will get better. Google Talk is a nice bell/whistle for the other components, but not something that would be a deal breaker if it weren’t included. It’s interesting to see that Google Spreadsheets and Writely are not currently included as part of the suite, but I guess the push right now really is “Gmail for your domain” and not “Google applications for your domain.”
You can’t beat the price.