First, I am a guitarist and cellist. Second, I'm a closet drummer (like most guitarists). I enjoy the keys, but am a woeful keyboardist. As a composer, the production of scores for television and games is one source of income and one day I will compose for film as well. However, I've had a recurring problem with scores, seeing as it takes me a fortnight to produce any given part for orchestra or whatever. So, I'd been exploring the possibilities of a MIDI interface that would allow me to utilize the many scoring software programs available (Sibelious, Nuendo, sonar, etc.). I'd read nightmare story after nightmare story about Guitar-to-MIDI converters, saying that they don't track well or aren't useful in real-time. Well, on a whim, I went ahead and bought a "Roland ready" Mexican Statocaster and a Roland GI-20 Midi-guitar interface as a combo on eBay just to see what I'd be able to pull off and am happy to report that not only does it track well with proper setup, but it has completely changed my approach to computer composition. Instead of laboring through a score that might eat up two weeks, it can now be done in hours. A big bonus is my ability to produce drum tracks with my fingers as well (killing two obsessions at once).
There are a few work-arounds for composition. The first being that when you record MIDI tracks, you do produce many unwanted notes that have to go in and delete before you print a score, lest you have unintended grace-notes showing up on paper. Many of the notes, however, are practically inaudible and not detrimental to performance. Also, you must carefully choose patches for performance, seeing as the afore mentioned grace notes tend to "re-trigger" the sound and produce unsightly artifacts. Piano and organ patches work great. Finally, the pitch-bend algorithm should be used sparingly and with caution as it can produce some weird out-of tuneness. I haven't quite figured out how to use it right, I guess.
Over all, I honestly think my computer experience will never be the same. Don't listen to the naysayers (Miles being one) who say that you MUST play the piano to effectively score something. Current technology is crazy and will only get crazier. I can't wait for the future.