I found out that the Computer Language Benchmark Game has some performance data for JavaScript on both V8 and TraceMonkey:
http://shootout.alioth.debian.org/
You can compare the performance against other language implementations for the same benchmarks, such as G++:
http://shootout.alioth.debian.org/u64/benchmark.php?test=all&lang=v8&... http://shootout.alioth.debian.org/u64/benchmark.php?test=all&lang=tracem...
Apparently this was run under a recent version of V8. It's nice to see that there's still a significant performance gap, and hence room for improvement. The pidigits benchmark is one on which both implementations do extremely poorly.
- Maxime