Ars Technica just did a review of the much-anticipated update of the Nexus One to Android 2.2 (Froyo) and the peformance improvements have been quite good. They ran the typical speed tests in the browser including the Google V8 benchmark and the Sunspider benchmark. The big surprise was that the Nexus One now bests the just-released iPhone 4 in these same tests by a very wide margin: over a 3x better score in the V8 benchmark and nearly twice as fast in the Sunspider benchmark.
Google's aggressive development efforts are moving Android forward at a rapid pace. The platform has matured considerably since its initial launch two years ago. The introduction of a JIT in version 2.2 has largely resolved Android's performance problems, making it more competitive than ever. As Google works towards version 3.0 and a rumored user interface overhaul, it's likely that we will see even more innovation.