OpenDNS?

I posted another question but that was not opendns related apparently.
Therefore this new question:

Hi,

I stumbled upon OpenDNS, what looks really intresing to me to use at home network.
Now I have some practical questions:

-could you explain the general use, I'm not sure if I get the full picture of opendns
-is there a way to "unlock" for certain profiles, even if I setup parental controls for some sites?
-can this be used to add DNS-entries for my home pc's so I can resolve them (now my router is DNS, dhcp hands out my router as DNS, can I replace this with the opendns)?  

Thanks!
J.