Google for Domains is just like Gmail...with additional domain features - e.g., you can create a number of users under your domain, you can control look and feel. It also includes support for a range of other Google apps (e.g., Google Docs, Google Sites, ...).
The email portion works just like Gmail in terms of the web-based client and the API that allows phone access with a native phone client. I have a Plam Pre and used the phone's native email client in the past to connect to my godddy account and a gmail account. The Google for Domains account configuration on my phone is the exact same as my old Gmail account. I also know folks using it with iPhones in the same manner.
Just like GoDaddy, Google for Domains supports POP and IMAP...so you can also use a fat client on your PC...like Outlook, Outlook Express, or Thunderbird, rather than the web-based client...but unlike GoDaddy, they do not charge extra for IMAP.
They also have a great forums area: Google Apps Help
After switching, I have no regrets. I love being able to delete (or mark read) on either my phone or PC and have that status convey to the other device. The web-client smokes GoDaddy's web client. The only oddity is (just like gmail) you cannot sort your "folders" (e.g., inbox) by "column". Very odd...but I suppose that they feel that their search and filter capabilities are powerful enough that this capability is not needed.
I suggest giving it a shot. You can always switch back. The Google for Domains account is free...and changing your MX records is pretty easy. You can point them toward Google and leave your GoDaddy email running. If you don't like Google, you can always point them back toward GoDaddy.
Either way, good luck!