It is easy to use all of the free goodness of Google Apps for Domains (GMail with IMAP/POP, Calendaring, shared Docs, etc.) AND use DNN for web content.
Here's what you do for a new domain (if you have an existing domain the instructions are slightly different):
1. Install DNN on your web hosting account. Add the domain name (both "domainname.com" and www.domainname.com) to Portal Aliases.
2. register your domain - it is easier and faster if you do this through Google Apps (which uses eNom.com) but you can use any domain registar.
3. Signup for a Google Apps for Domains account here: http://www.google.com/a/help/intl/en/admins/editions_spe.html
4. Login into Google Apps, click Mange this Domain, then click Domain Settings > Domain Settings > Advanced DNS Settings > click the link to open eNom.
5. Edit the "@" entry (A-record) to point to your DNN installation's IP address.
6. Add a New A-record "www" to your DNN installation's IP address.
7. Depending on your DNN host account there maybe some other DNN settings.
8. At this point the following URLs should work:
- www.domain.com and domain.com ----> should open your DNN installation
- mail.domain.com -----> Gmail (name@domain.com)
- docs.domain.com -----> shared/private docs on Google
- calendar.domain.com ---> shared/private calendar on Google
Enjoy!