I haven't been on the forum in a while, and I see there seems to be less and less traffic. Maybe that's just the circles in which I run!
A company I work for has hundreds of slingbox devices in the access directory, made up of newer (SB500/SB350) and older classic devices. We primarily use both the web access and the older desktop client for Slinbox connections. I have never heard of any numerical limitation, but with the PC client s/w, starting with vs 2.0, the device directory is not on the PC, and has to be downloaded. Sometimes that download is very slow and take a while before the directory access pops up on the screen. Realize, that is with hundreds of slingbox devices, not just a dozen or so.
Of course, I have had recent problems with the Newwatch web connection. it will not allow me to select, and therefor connect to any device. Have you seen that issue lately?