*hangs head in proper chastisement*
Sorry, Cath. If you wanna bonk me, feel free.
Will -- I've not seen these threads, but I'll offer my two cents anyhoo...
-Make sure you and your beta reader(s) establish what each of you wants out of the relationship before you agree to work together. Find out if they want reciprocal reads, and let them know exactly what kind of feedback you're looking for. Example: maybe you want plot holes pointed out, you're trying to see if your flow works, want some general thoughts on your characterization, desire to have every misplaced comma pointed out, stuff like that.
-Also ahead of time, decide how you'll transmit/exchange your work, how much of it you'll work with at once (chapter at a time, 50 pages at a time, the whole shebang) and work out a reasonable time frame for when your beta will be able to send his/her feedback. Having an approximate deadline helps to make sure there's a little urgency to the read, so it's not shuffled off to one side as "when I get around to it."
-Read a sample of their work first, and offer to let them read a sample of yours, to make sure you're both comfortable with each others' style and subject matter.
Good luck (no poking this time!)