Otlecs,

While I can't get technical with it as I haven't read up on symlinking in a few months, I can give you my experience. I have a Velociraptor HD and I ran all 5 accounts on 1 machine, in 3 install directories (main1, slave1 & 2, slave3 & 4). I hadn't symlinked and I was noticing lots of long load times hearthing, etc and lost-follows in heavy traffic areas. Once I symlinked my data and interface folders in the 2 slave installs to the main install, all of this virtually disappeared. I never again lost follow in Shat (haven't boxed in WotLK yet) and the longer load times across the toons (addon & data loading basically) returned almost back to the same as when I was soloing.

It's good to have the separate installs so you can assign multiple cores in keyclone, and I'm sure there's other benefits, but you do raise a good question. I would imagine each user would see different results depending on their system setup. For me, symlinking was a huge improvement!