Generally, I just use my own (co-located) DNS server from my laptop. However, I sometimes run into problems with wireless providers away from home, especially at airports: sometimes they have it set up such that you have to log in or pay at a URL that they expect the local DNS resolver (which their DHCP will have handed you) to resolve to the local server.

So, for example, foo.someprovider.net when resolved at City Airport using the local DNS server will point to an IP handling payment/login for City Airport, but the very same hostname foo.someprovider.net at OtherCity Airport will resolve to a different IP that happens to be the payment/login server on the local net at OtherCity Airport.

I've run into other instances of this. Basically, not taking the DNS server that DHCP hands you, sometimes causes problems. Usually you can figure out what's happening and change your settings, so it's an annoyance rather than a real failure.