I'm currently having 2 problems after the dash update...
1. 1080p support not working. I've now got every output kit that MS makes for the 360 here, and I cannot get 1080p to work on my 1080p TV. I phoned HP, and the idiot on the other side insisted my TV was fine - obviously both the 360 AND the PC I've connected to the VGA input on the TV are broken and are not sending a proper signal. So right now I'm running the 360 at 1360x768 which is the highest resolution selection available that works. I could switch back to the component kit for 1080i I suppose, but in the long run I want VGA to work as there's no DVD upscaling over component.
2. Streaming video with Media Player 11 does not work. In fact, since upgrading to media player 11 picture and music streaming stopped working too. I called MS about this one, and they couldn't fix it. I did learn that using a gigabit switch to connect the 360 to a PC is not supported, only routers and crossover-cables. I also learned that MS is having a LOT of problems with this dash update, and that they will likely be releasing a patch for it in the near future.
I complained to MS about the 1080p thing too - apparently that is one of the big problems in the dash update that they have to fix. There is some type of timing issue that only affects certain models/brands of TVs.
Guess I'll go finish rebuilding my HTPC - it doesn't have the CPU power to display 1080p content without dropping frames (or even 1080i in any codec more advanced than MPEG2), but at least it can stream music and SD video over the network and output it at 1080p60.