"I honestly never succeeded in creating a decent solo string part as a final product. I alway's hire musician in that case where interpretation is crucial and complexe." - FredB
This statement is somewhat annoying to me. Partly because this could simply be due to your inability to do a MIDI performance, rather than a problem with the library. And partly because it is obvious if someone hires a player who is really good, then they will probably be good competition to samples.
However, my experience is very different. I came from a classical background, was a professional orchestral player on horn for twenty years, and had many live performances of my own works. But I have never had as good a performance as what I have recently done with VSL. In fact, I released a song-cycle "Earth and Paradise" - http://www.cdbaby.com/cd/williamkersten - which was premiered by a chamber orchestra live in a large concert that was well-received and reviewed, but the playing of the orchestra simply was not as good as VSL, and so I re-recorded it with the soprano and VSL for this CD.
Statements made by people here about how a live player is always better mean very little, since it depends on how good the MIDI performance is, not necessarily on the library.
Though on the original topic of this thread, I agree more samples are always better.