Too difficult to manage. Cases in point:
1. As mentioned before, too many pages to check out.
2. Transfer lock is also domain modification lock. Can't keep domains locked and still make DNS changes. To change DNS on a locked domain, you have to select, unlock, wait 1-2 minutes for change, select domain, click change DNS, activate fields (WTF?), enter new DNS, submit.
3. Too commercial. For a real domainer, you don't need glamour (what's with the girls everywhere?), graphics, and upsells. You just need to be able to register domains quickly for a good price and manage them easily. Godaddy fails on both counts.
4. Absence of any good DNS management features (a la eNom) other that redirect.
On the other hand, I do like their domain backordering, now that they give you first dibs at Godaddy-registered domains. Hope they keep this around for awhile, as I have dibs on a few domains that should make the pain of this registrar worth its while.