If you come across a great sounding remix that has been put together through a whole set of contributions (e.g. drums then keys then vox then bass, then gtr) do you give a thumbs up for just the end result or do you go back and give a thumb to everyone in the chain? Or maybe just those whose parts you thought were particularly good? (I'm sure we've all heard great parts on bad tracks and vice-versa!)
My own view on this as a 'thumber' is... inconsistent. Sometimes I'll give a thumb for a particular part I like, other times it's the overall sound and I'll try to give thumbs and comments to everyone involved. I suppose it also depends on how you come across the track- often I'm listening to a particular player out of curiousity because they might have given me a compliment so I'm very much hearing the part rather than the whole.
As a 'thumbee' I choose to believe that thumbs and compliments on remixes are an indirect reflection on the part I've played so don't necessarily expect anyone to pick out my 'layer' (The fact that someone has done a remix in the first place is a huge compliment!)
To be honest, this is nothing new for rhythm players - we're used to standing quietly in the corner after the gig while the singer or lead guitarist is mobbed but one of the interesting things about wikiloops is that oftentimes the 'normal' recording order is reversed with the 'lead' parts going down first. :)