I used to find that I'd get slow downs when performing requests because the ISP wasn't answering the DNS query in a timely fashion. This would usually resolve itself in half-an-hour or so, possibly a load issue. But with OpenDNS I've not had those problems, my ISP nameservers are there as backup however if I should need them.

Also OpenDNS optionally does filtering and allows reporting of lookups made. As my kids grow and explore for themselves I think this will be useful.