Roughly same as William and Frederick...
I personally think the Solo Violin is amazing. In fact, if you write a truly idiomatic passage for it, and change articulations frequently, it's almost unbelievable. I'm using it right now just for composition. I've got a little Max/MSP patch that does some interpretation for me, and I run from Finale on a Mac through to VSL on a Giga PC. Even just with this composition setup I'm finding the Solo Strings to be very impressive. I think you just have to be very carefull in the sample choices you make. For example, I'm finding that there are many times when I'll use a "prog-vib" or "port 0'5s" sample in place of what might otherwise just be "ord". This gives the line some shape, and varies the sample selection, making it harder to recognize direct repetitions of a particular sample. Anyway, if you take some time to create an all-round instrument, with all the articulations you think you might want to use, then it doesn't even have to take a great deal of "programming" during the composition process -- just the occasional test of a couple of different possible articulations, and go with the one you prefer. I'm very happy with them. In fact, I'm pretty sure that in the right instrumental setting, and with some careful composition, I could fool a great many people into thinking the VSL Solo Violin was the real thing!
J.