It may depend on the film you are watching. If you are seeing "Sound By" then I would imagine that's an independent film?
Unless things have changed, I'm almost certain that most of the big Hollywood studios have agreements with players' unions that they have to use live orchestras in the scores at least to a certain percentage. In which case, VSL may only be used for mock ups. Unless, it's a purely electronic score and even then there are some stipulations.
The independent film world is a different story however. If you watch a lot of independent films you are probably hearing VSL, Eastwest, Synthology and others. It just depends.
I think if you go to the "projects" page of the VSL site I remember reading an article about Paul Haslinger using VSL to score Underworld. But I don't remember much else about it. I was just interested because of Paul Haslinger-of Tangerine Dream fame.
I have kids and with kids come video games. I swear I've heard VSL strings in the Halo video game series.
Here's an article you might find interesting:
http://www.timespace.com/features/669/top-film-and-tv-composer-reveals-the-products-behind-his-compositions.html
Although I must say that I've never heard of the composer, here's a quote from the article that the VSL might find encouraging:
Miguel D'Oliveira-composer of film and TV
"In terms of future virtual instruments, is there anything you´d like to see that as far as you´re aware hasn´t been done already?
I’d like to see dynamics get better. Fortissimo still lack that extra shine and oomph – particularly in brass and strings. But most virtual instruments are already absolutely amazing. For example, whenever I get a clarinet player to replace my VSL clarinet tracks, they usually get very intimidated by the VSL sound. It can even fool clarinet players at times thinking it is already a live track. But even with small flaws, I always prefer to have a few live performances amongst the VSL bulk."