Been over a year since my last response to this thread... I'm still offering free samples, even tho I definitely don't need to anymore. They are offered with a stipulation that they will only get done in my free time (such as it is), and I'm under no obligation to get them done according to any kind of schedule.
The reality is that I can only get to about 10% of the tracks I receive, and most clients have to make a choice before I can get to their track. It feels weird to offer something that I usually cannot deliver on, but then again, it *is* something for nothing. I don't feel too badly.