Haven't yet done the upgrade to Mountain Lion as some writing for the fall and the indoor season is still going on.  Any word on compatibilty with all of these?  Anything else I need to check out before making the upgrade happen?  Other things like Kontakt, The Write Score templates, etc.?

Thanks for the help, all!

Kontakt 5 is working well with Mountain Lion. If you're using VDL library 2.5.5, that's what I'd recommend.

As for your Sibelius 7, you'd have to check with Avid for compatibility. I believe it's working fine, but they'll have the official word.