I am wondering what actually motivates people to contribute to these backing tracks...???

For me it is genuinely to be able to put something reasonably advanced together over a backing track that I don't have to worry about and be able to hear the different takes that other players have on the same piece of music. Sometimes I hear a phrase or part on one of the other takes and think "wow that works really well" - I find the thread helps to get new ideas and viewpoints in terms of how others see the same piece of music. That plus it's nice when you get positive feedback but equally important when I hear negatives - I still play what I want to hear but sometimes you realise something is off when a fresh set of ears hear it and leaves detailed comments. If I don't like the backing track or it doesnt inspire me then I don't bother recording anything.

Anyway, I havent been able to play any of my guitars for about the past 15 weeks becuase of a big job in my house. Moved back in over a week ago and it still won't be finished untill next week. The work included a sound treated recording studio in the attic so I will be back with a vengeance once the damn contractors get the hell out of my house!