If for whatever reason hosting provider freezes the account, and you have domain regged with them and dns setup with them... you are screwed. OTOH, if you have it all separate, you have options. Get with a new host, repoint your dns, and done. Plus, zoneedit rocks. It's not totally free if you have over five domains w/ them. Plus they do (for $) nice extras like MX (mail) backup service.
As for speed... it's just as likely the client's ISP has a crappy, overloaded DNS server doing relaying. Anyway, once the client caches the initial lookup, that's it for a while. It's not like a 2-3sec hit each time the page is loaded.