If you got iTunes or Safari you probably also have a map called ´Bonjour´ in your ´Program files´ map.
Rename this Bonjour map to whatever you want and reboot your pc... start your launcher and probably it starts downloading the patch!
Ive tried this twice and for me it worked.
Why this might work?
When you start your wow launcher it also boots `mDNSResponder.exe` on the background which works with IP-protocols to make for example your iPhone work better with your pc if you use internet thetering (correct me if I´m wrong). This might conflict with the launcher. mDNSResponder.exe works with UDP-port 5353.
I´m no expert so everything just seem to be a logical guess.
I´d be happy if it can be confirmed or if it helped anyone out :)
This is after last update, 31/08/11
moral of the story try run as administrator before reinstalling.
hope i helped :)
Although how did you find it?