* The purchase of webfaction w/ a promise to migrate sites to a new host. They promised for over a year to do this migration and then 30 days before shutdown told me they could not migrate and to figure it out.
* Domain name sniping. Never ever use godaddy to search to find a domain. They will just steal anything you search for if you don't immediately claim it.
As a customer, I highly recommend Dynadot (low prices like NameCheap, but a nicer interface - I tried both registrars when I switched my domains away from DreamHost).