stevec
VST Expression also has to be supported by the instrument itself, so I would check that the ones you want to use can actually take advantage of it.
I don't think this statement makes any sense in terms of what an expression map does as I understand it anyway. It's true that not every library may be mapped the same way, and every library may not be pre-mapped, but the way I understand it (only from being told by folks that use it) is that you can create your own expression maps, so you can map note information for key switch articulations, you can map CCs for instrument controllers, and you can even use midi-learn from your VST instrument and simulate a CC knob/slider movement to map a particular CC to the particular VST instrument control, and the expression map and lane expression data supersedes any other MIDI data going to the VST instrument.
Once you are mapped, then, you can freely draw CC information for any number of tracks without affecting other tracks, and you can use note expression to manage key switching. Essentially, the DAW's expression map supersedes any incoming midi data for that track/lane, so now you are no longer limited to 16 midi channels for controlling your VSTs.
And if you think about it, you can already to that pretty much with note data in Sonar (minus the nifty note expression symbols, etc), but you can't do it with CC data (at least I haven't found a way to do it--please, please correct me if I am wrong because I don't want to migrate to a new DAW).
My experience is that Sonar forces me to choose a channel for a CC, and once I do this, that channel/CC is marked in use for the whole project, and that CC will affect every instrument on that midi channel that responds to that CC. If CC data were to remain local to the track or to supersede incoming MIDI CCs if written to a track lane, and if every track lane could re-use MIDI channel CCs, there'd be no reason to move, and that's leaving out the nifty expression map note data and the fact that helps when you are printing out score notation.
At any rate, I am primarily looking at this as a way to simplify workflow for Kontakt-based instruments, and that's what the folks using Cubase tell me about VST expression. The devil may be in the details, but there seem to be a lot of people sold on this, and they are using it for a reason, and that reason isn't--I don't think--that they are just Cubase fanboys.