Why do you guys create separate wow install directories? I been running from the same install no problems.
I'm a recent convert to the whole "multiple WoW on a single machine" thing, and gave this a bit of thought ahead of deciding how to handle it.

Apart from the potential for file access problems and data corruption / loss for any mods you might be using, the single most important thing for me is unique key bindings per-instance of WoW.

On each of my machines, I have a "WoW Master", which has all my regular keybinds so I can play any of my characters directly, and one or more "WoW Drones", with fewer key bindings (like movement keys unbound for example).

Apart from my multi-boxing, I still enjoy playing a single character from time-to-time and that would be close to impossible with my personal key setup because it's quite different between the master and drones.

I keep everything up to date with a simple sync relationship across machines and across installations. Update one, sync binaries, all done.

I'm glad to hear a single install is working for you though. If it ain't broke, don't fix it

To the OP... let us know how you get on with that machine. I don't recall seeing any specific metrics for this sort of thing other than my own experiment with 5 WoW running on a 2Gb Vista laptop when somebody made the mistake of telling me it couldn't be done