www.adoptionguide.com (think I got that right) is a good site that runs tabs on agencies, and is driven by member feedback. You do have to register but it's free.
Also, you can go to "open houses" like April said. That will give you a 'feel' for the workers there. ANY agency should give you references you can contact, if they refuse, then run the other way.
you can also check the Better Business Bureau (online, even) to see if they're listed and if they have any charges/complaints against them.
You can also visit
www.forums.adoption.com which is a very large website to ask other folks and get feedback on who they're using.
I must say, tho, that your gut feeling and instinct is a major factor. Remember, you're interviewing them, they work for you...not the other way around.
Can't help on the domestic thing about how long parents have to change their mind, since we bypassed all that by going international. I've seen a list online somewhere that has that, but I forgot where. Maybe someone else here can point you in that direction.
A good source of info would be to contact an adoption attorney. Someone in the office can probably give you that state specific info or at least tell you where you can find it.
Good luck!
Robin
Adoption questions 
Thankyou 
