[jwr]

Speaking as someone who designs hobby electronics, this is a very good idea. I can't count the number of times I had to type things like "mcp23018 eagle library" into google. And get no useful results except link farms. And then have to create a library part in Eagle, which is a painful process, thinking all the while that many other people are probably doing the same thing right now.

I will definitely be contributing my libraries.

[keenerd]

You should try Kicad. Similar problem with libraries, except making new footprints is my favorite part of the suite. It is a pleasure to use.