I've played with Sonar's surround support and over all it works pretty good however it does have a fairly large issue in not supporting surround VSTs. It seems to want to use a bunch of parallel 2 track VSTs. This means things like the Waves 360 tools won't work. It does make surround mode a bit less useful if you can't get true surround effects going on.

Yes. I would love to see full surround support.
 
And there are also other uses for surround VST's than straightforward surround processing - for instance using things like an NI Reaktor ensemble to process multiple tracks simultaneously.