How do you decide what DNS addresses to use on your server and clients?

I was going through some clients at one of our branch offices, and noticed that several had up to 4 different DNS addresses listed in the IP configurations...I had a guy that WAS suposed to be taking care of that stuff at that particular branch, but I don't think I'll trust his judgement any more...

I pretty much a newbie at this network admin stuff, so is there a correct or incorrect way to configure those DNS IP addresses???

I know that some of the addresses seemed to slow the user's logons to the network when they first sign on to the network...Probably because the DNS servers referenced were bouncing back the IP Packet equivelent of "I'm searching, searching, searching...Sorry, no idea what you're looking for".

If you could explain this IP configuration thing in english I'd love to hear your input!