Thanks Dan!  I did install it today, and I'm finding everything you said to be exactly true for me as well.  Rendering on my 2.33 Ghz Core 2 Duo MacBook Pro is only slightly above half of the speed of my HP Windows laptop with a 2.0 Ghz Core Duo (on the exact same scene).  So I'd evaluate the relative, cycle-for-cycle performance to be cut by up to 70% by Rosetta.
All the same, the performance seems good enough to allow me to do some scene design and modeling on my Mac, and that's a good thing, since that's the machine where both Photoshop and my video editing software reside.  I'll be doing network rendering when the time comes for lengthy final renders anyway, so both machines will get to participate.