I am not using a Revo/Ion setup, but an htpc that I built myself that should be a very capable Boxee setup. But I must admit that I am very frustrated with getting hardware acceleration work.
My machine's processor is an AMD Phenom II 550 BE dual-core 3.1 ghz with 2 gigs of ram, running Windows 7 32-bit and a Radeon 4350 video card. I have a 6mb DSL connection. Hulu desktop looks pretty good but I seem to be experiencing slowdowns in frame rates. No audio stuttering. My two other machines (a Phenom II X3 triple core and Phenom II X4 quad core) act the same way and all 3 experience similar processor usage with hulu Desktop (about 45% on average).
I have spent a good bit of time updating the various pieces as described in this thread but I can't seem to see any difference in overall processor usage. I have verified that both IE and FireFox are reporting the 10.1 version of Flash, the video card's driver is the most recent, etc. but no dice.