I'm thinking of a few ways to break it into smaller pieces:
Region: NE, SE, midwest (plus OK and TX), West (including AZ and NM) and Canada/overseas. That would leave each US region with 11 to 14 states.
Timezones: east, central (with TN and KY), and west/mountain/AK/HI
Species: warmwater states and trout states.

Thanks to everyone so far who has spoken up. I'm trying to think my way through this as we go, and I'm getting some great ideas.

Another question: Would everyone be more or less willing to sign up if there was more tying to do, but you would get a complete set vs. tying 1 or 2 dozen, but only getting back a portion of the entire project? I personally would prefer the whole set (it would be cool to build some sort of display out of it). If it was broken up, it could be hosted by multiple people. I can handle the whole thing, I think, but if we decided to break it up, it could be fun to spread things out to each region.