I wouldn't mind slow load time launching Zune MarketPlace for the first time. But I would hope the did some caching and prefetching so subsequent loads are much faster.
I wonder if you have to go back to the Kinnect enabled dashboard anytime you want to get into particular content area like Zune MarketPlace, Netflix, etc. It would be great if you could say ex. "XBox..Goto NetFlix" anywhere/anytime to jump around.
Windows 7 - Gateway Laptop, Windows 7- Gateway Desktop - Dual 22" LCD
Windows 7 Media Center - HTPC homebrew, Dual Tuner
XBox 360, Zune 120 and Windows Home Server - HP MediaSmart (3 TB)