I would like to report two problems.
First problem:
Regardless which computer (A, B or C) is the master, the two slaves can only share the clipboard with the master, but not among each other. (I get "Shared Clipboard Data Unavailable" messages.)
Second problem:
When computer A is the master, then I regularly get a "Slave system failed to respond. Do you want to skip this slave" error for computer C when the cursor transits to computer C or when I scan the slaves. After some testing I found out that this happens, when computer C is more than about 40 seconds idle. Immediately after clicking the "No" button (for don't skip), the transition/scan works again without error. I increased the "time to wait for a slave to respond (in seconds)" to 10, without success. It seems that the scan or the attempted transition wakes up the slave and gets thereby swallowed.
Perhaps some strange power saving service of Windows 7 is responsible for this behaviour; however, I think Input Director could take this into consideration by not only waiting 2 (or 10) seconds for a response but instead sending a second request to the slave, if there's no immediate response to the first.
Remark: If I disconnect computer B, i.e., if there's only computer A (master) and C (slave), then this problem does not occur.