Writing an apples-to-apples benchmark comparison of two very different serialization frameworks is apparently hard.
In my first attempt to compare serialization performance of Jackson JSON and Google Protocol Buffers, there wasn't a huge difference. After some suggestions, I made some revisions and found Jackson to be much faster than Protocol Buffers.
A bug was recently found in the benchmarks and the effect of this bug gave Jackson a pretty unfair advantage. As you'll see, fixing the bug leads to a complete 180ยบ in the results of these benchmarks.