Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
Developer Transition Kit Benchmarks
Here is one XBench screenshot showing the developer 3.6GHz Pentium 4 PowerMac running Xbench under the Rosetta emulation. Screenshot
On the left is the Xbench under emulation and on the right is Xbench running on a Dual 2.7GHz PowerMac G5. This simply shows that Rosetta certainly works, but is hard to give us real performance comparisons until the final shipping machines come.
ThinkSecret notes that the Intel Mac scored well in both the Quartz graphics and OpenGL graphics tests "almost matching or exceeding dual-2.5GHz G5 score".
Readers should note, that while all PowerPC native instructions are translated/emulated, since the underlying Mac OS X is running natively on the Intel processor, system tools calls/APIs should enjoy native (not emulated) speeds.