I encourage you to listen to jokull, and find out if JSON really is too slow for your needs. My advisor taught me that if you keep your data in an easy-to-read format, you're more likely to catch bugs in the output, merely because you have first-class tools for inspecting the file and are more likely to do so.
I find protobuf easier to catch bugs, because it can catch if you're missing data or trying to put the wrong type in or leaving out a required field. There is a ascii-version that is more readable than JSON, too.
That said, overall I agree with your overall sentiment, certainly do look at JSON as well. Protobuf is overkill for a lot of things, and JSON keeps things simpler.
I also have some benchmarks of Python deserialization of JSON, and talk about alternatives here: http://blog.metaoptimize.com/2009/03/22/fast-deserialization...
I encourage you to listen to jokull, and find out if JSON really is too slow for your needs. My advisor taught me that if you keep your data in an easy-to-read format, you're more likely to catch bugs in the output, merely because you have first-class tools for inspecting the file and are more likely to do so.