The one thing that sets VSL apart from everything else out there is the performance options built into the VSTi.
The sound of the appassionatas overall is pretty good (way better than the original string samples by VSL) but there are issues (pheeping noise) on some of the notes which I find sort of unacceptable in a € 1000,- library.
The real downside in my opinion though is the way the plug-in performs.
On my system (Dual G5 2.0 Ghz, 4.5 GB RAM) I get drop outs and clicks and pops with just one instance of the VI. Also unacceptable. I have to pretty much freeze everything in order to hear what's going on. Very bad if a client sits next to me and I have to apologize all the time.
Unfortunately there isn't more competition out there or else VSL would have to get their act together and provide a better and more usable product.
Although I spoke with the support person at the Musikmesse I feel that I wasn't getting the value for the money that I was come to expect by all the reviews. to be fair: yes, I still use it in all my tracks, but it does break my flow and inspiration because of it's stability issues.