For those that don’t know, Google now offers web based applications. One of the offerings is free hosted email services for your existing domain, and for up to 50 accounts.
I have been slowly migrating my domains over to this service, with and without using JodoHost email services as a backup fail over. So far I can rate this service as very good!
If you’re interested in checking this out for you or your clients, click here.
I have a domain using it to test as well 
I’ve been using this October or so and it’s really nice 
The space is a godsend as well
I have a post here with some tips on the transfer:
http://support.jodohost.com/reseller-support/8430-gmail-hotmail-domains-2.html#post46173
Also, google just added a way for you to set a DNS CNAME and forward mail.domain.com to the google mail service.
Yeah, this is what I have been doing for my clients. All mail service is now routed to their own domain’s branded gmail service, including brandable login page, and includes all the features of a regular gmail account, webmail and pop. I do wish they had folders though, but the search function does work really well.