"If you publicly use any adapted version of this database, or works produced from an adapted database, you must also offer that adapted database under the ODbL."

It's basically a GPL vs MIT issue. A lot of people think GPL is better for great reasons. A lot of people think MIT is better for great reasons. I fall in the latter camp.

http://opendatacommons.org/licenses/odbl/summary/

I was going to write that I thought it was silly to convolute software licensing with data licensing, but I can't really find any fundamental difference between them.

All that does is prevent Google from slurping OSM into Google Maps and not giving anything back. I don't see how it prevents it from being "usable and useful". If anything, it makes it more useful because if everyone contributes to OSM, it means we're not constantly reduplicating effort.

Like I said, it's the same debate as GPL vs MIT which has been had on the Internet a million times.

Symbiotic vs Parasitic describes it better.

A million and one.

A more damning criticism of OSM licensing is that it's incomprehensible. Let's say you want to create something based on OSM data. Do you have to make your creation available under the ODbl? You can subscribe to the legal talk list if you want to see a parade of people trying to figure out how it works.

More practical is to just armchair-lawyer the terms and just hope that nobody gets upset with you.