Umm... just thought I'd chime in here even though I'm new and ya'll don't really know me or have a sense of who am I personally or musically ('cept you Kev!)...

I think, perhaps, that what you have here is a misunderstanding and an incomplete reading of the situation. As Kevin points out (and if I'm reading between the lines correctly myself) the backing tracks and instrumental pieces that Letha has become inspired by were created by (and in a sense, very much for...) the members of a small, relatively private community of online guitarist jammers for "their" own enjoyement and recreation. I mean: heck it's a bunch of guitarists laying down four minute solos afterall! crazy

As he says too, once a backing track "goes out into the world", especially via the intermediary vehicle of Soundclick hosting, the backings are for the most part available to anyone that finds them. Minor caveats: one must be a member of Soundclick to download them, and one must be a member of the guitar jam site(s) to be notified of their availability. Most of the members of the communities where I participate use a creative commons license for the BTs, not so much to protect their work but to formally grant permission to anyone to do with them what they will.

I mean no disrespect and intend nothing other than to relate what it sometimes feels like on my end, from the other side, but when someone from outside the original community of my work/playing contacts me with a desire to do something, my hard-earned experience has often lead me to be wary. When I post a BT in that community I'm explicitly inviting other guitarists in it to lay something down on top of the BT. I'm not, really, putting up a "Looking for collaborators" notice all over the web. I'm very much paying them back for all the tracks they've let me play over, because I'm one of the subset that can actually create them.

That said, I and most others generally appreciate being contacted when someone wants to do something different -- but in my experience it can often be a Great Unknown, since you don't really know the person making contact (in the way that you "know" members of your own community), you don't know how much involvement from you that they might be seeking, how they might respond to your advice or counsel, or even how technically skilled they might be at protecting the quality of what you've done already as the track evolves through their own work. In my experience these are not non-issues, and my answer or response to an inquiry on any given day, though it might seem whimsical or terse to someone that doesn't "know" me, depends much on my mood at that moment (and theirs), my reaction to any draft that's included in the request, how much time I'm willing to devote to the work, the correspondence, the actual collaboration, etc. -- all that gets weighed.

"Laying something down" on top of a backing track (whether it's guitar, bass, rhythm or lyrics and voice) is in the end very different from true collaboration -- and I think it's wise to keep that difference in mind.

Over the years, and most definitely out of a desire to protect those things that have my name attached as my skill allows, I choose to either be in for a penny ("do whatever you like and have fun", i.e. turn down any expectation of collaboration) or in for a pound ("please let me help you make this work for both of us"). One takes a moment, and the other can take hours and hours and hours, and often with some or all of the issues I mention getting in the way. If you're the BT person, it's sometimes most appropriate to say "You already have my permission, but I don't want to be involved in what you do". BTs are sort of blank slates though. If lead instruments are already there when the vocals arrive, then "doing it right" is even more complex and time-consuming. Not everyone has it when asked.

'Hope that helps a little. All you can do is ask, and then live with the answer...