... TAKE A NOTEBOOK... AND WRITE THINGS IN IT!
It is quite likely that your prospective agent will have some Pearls of Wisdom to impart. (I wish there was a PoW shop... ten for a pound perhaps?) Prospective Agent may well tell you some things about your manuscript that will make you want to bang your head on the table in a why-didn't-I-think-of-that? manner. Prospective Agent has knowledge that you do not. And if you don't take notes, chances are you won't be able to remember what he/she said in sufficient detail. That would be bad.
My agent, Marvellous Victoria, has mentioned that the fact that I took copious notes during our meeting went some way towards her taking me on. If a prospective agent has gone to the trouble of reading your manuscript (maybe even more than once), the least you can do is take notice of what they have to say. I can't stress enough the fact that they KNOW stuff. Of course, you might know some stuff too, but probably not as much as they do. Trust me on this one.
And even if Prospective Agent doesn't magically transform into Actual Agent, you can still take away those Pearls Of Wisdom and make your mansucript better. That can only be A Good Thing.
You can find a very interesting interview with Nancy Miles, director of the Miles Stott Children's Literary Agency, here. Nancy was also at my meeting with Marvellous Victoria, and I wish all of you could have been there too, because it was AWESOME.