RIAA is indeed suing little girls for lots and lots of money, but to me this makes sense so far. It might be bad for PR, but it indeed has been effective in stopping much P2P. The RIAA might think a PR plunge might be worth that.
Why are people complaining about the amount they are sueing? From their point of view, you're going to want to scare them as much as possible. However, if this is kept up, eventually someone with enough cash and backbone won't back down. It might not even take as much as you think--it is rather hard for the RIAA to prove that said person was sharing copyrighted material, not to mention that no sane judge would let a coorporation get millions of dollars from an individual, assuming they had that much money. Otherwise, I guess they'd be sent to the juvie / prison.
"What you in for?"
"Brutally murdering 5 people in public. You?"
"... Uhm, sharing music."
"Whoa! S-stay away from me!"