I just switched out my Win7 HTPC install to Win8 this past weekend. It was the last PC in the house with an "old" OS with 4 laptops (both my wife's and my old laptops handed down to our children count as two) switched to Win8 and my WHS2011 server switched to Server 2012 Essentials.
The only difference that I can recall, besides getting the latest Win8 drivers/software, was needing to get a special version of MediaBrowser. Also, there is no "Boot Into WMC" option.
I installed StartIsBack to add back the Start button and easy boot directly into the desktop. I'd assume most of the guide would still apply, but I've not used it.