T-Mobile's G2 will have the new Snapdragon inside, sorry, not the dual-core one
The MSM7230 runs with speeds up to 1GHz, but, what's more important, is that it includes the new graphics unit Adreno 205, which should notably improve 2D/3D performance over the previous Snapdragon generation. Thus HD video encoding and decoding with 720p at 30fps comes standard, as well as HDMI-out capabilities.
Other phones with 45nm chipsets currently on the market are the Droid X and Droid 2, with their TI's OMAP family inside, and the US carrier versions of the Samsung Galaxy S with Samsung's Hummingbird chipset. The Hummingbird has the best GPU of them all, but what will see the biggest gain from moving to the 45nm Snapdragon is most likely the battery life, since that's what we are observing with the OMAP and Hummingbird-based handsets.
Also, the T-Mobile G2 will be running Froyo upon launch, so with the new chipset supporting the HSPA+ download speeds, it will be one of the fastest Android experiences on the market, at least until a dual-core phone is announced.
T-Mobile G2 Preliminary Specifications