It does look like you can use it to retrieve mail from GMail accounts. I didn’t complete all the steps, but the portion that tests for valid email addresses didn’t reject it (unlike invalid addresses, or your own GMail address).

As for Google Apps for Domain; I signed up for this a while ago to check it out, but didn’t switch. There were two issues;

Firstly only GMail, Docs and Chat are available to Google Apps for Domains accounts. Other services, such as Google Reader or Analytics, require a regular Google sign-in account. That means I’d effectively need to sign into Google twice, and would lose cross-app features.

Secondly; Even when using Google Apps for a domain, sending email from addresses other than the one tied to your account results in the ugly ‘on behalf of’ issue. For example I could be andrew@andrewgrant.org, but if I also needed to send email from blah@andrewgrant.org than that email would still include the ugly ‘on behalf of’ statement

As for the ugly “on behalf” issue, have you thought of setting up Google Apps for your domain? Essentially using native gmail with andrewgrant.org – pretty cool.