What is your general location?
Search Wikipedia for the OpenDNS server locations if they are near you or not.
Have you ran namebench?
https://code.google.com/p/namebench/
Try downloading something large from Apple and time it while on OpenDNS, then swtich back to your ISP DNS and download it from Apple again and time that, compare the results.
A alternate DNS server has to be in the same general vicinity as the ISP Internet server because Akamai content (Apple uses) goes by DNS server location, not by the users location closest to the ISP download server.
http://apcmag.com/why-using-google-dns-opendns-is-a-bad-idea.htm
Many recommend a alternate DNS service as a workaround to a ISP DNS having issues, but OpenDNS and GoogleDNS (and others) also have issues too.
If most people just waited a bit, the problem gets resolved and they don't need to suffer adverse effects (and privacy issues) of using a alternate DNS service unnecessarily.
There is nothing wrong with reccommending a alternate DNS, as long as it's for the right reasons and there isn't a costly side effect.