To be honest, on beta readers I've found that simply finding my own from the boards works MUCH better! I'll never forget the beta I found on the list who told me that I needed to EXPLAIN who Darth Vader was...and how he was related to Leia. I'd recommend finding a few people (I have about four people I call on) to beta read and keeping them. The list never worked for me. Of course, that may be an isolated thing pertinent only to me.