Well here are the instructions for the 7d with katzeye.
Doesn't seem too difficult at all - at least nothing that a good techie can't handle.
I wouldn't be too concerned about getting a focus screen from katzeye or focusscreen.com
for all the mf people out there.
yes, getting a good focusing screen isn't really the issue. it's voiding your warranty by installing it and the lack of built-in metering compensation that's the real problem, imho.
sure, i can buy and install a katzeye focusing screen, but then my metering will be off and there will be no way of fixing it. cameras that allow interchangeable focusing screens have built-in metering adjustments, which the Mark III won't have.