I bought 8 Pro + Media center pack for my new Haswell build (which replaces my old Bloomfield WMC based whole-house-DVR build), thinking that with Win7 active support ending in Jan. 2015, I wouldn't want to be redoing it and losing any DRMed recordings in only 15 months.
Let me tell you, this was a major disaster, and I ended up buying another Windows 7 license for it after giving up on 8/8.1.
Among the problems with 8/8.1:
USB doesn't work properly on Intel Series 8 (Haswell). The intel drivers for Windows 7 won't install because as the FAQ on Intel's site says "Windows 8 includes built in support for USB3" -- the thing is the built in MS drivers aren't really compatible, and a lot of devices won't work. 8.1 is better about this than 8, but still horrible. In fact, I would be the reason every Haswell motherboard includes a PS/2 port is because the keyboard and mouse won't work properly during the Win8 install process on USB. You can hack the INF and disable driver signature checking to install the Intel drivers, but Windows Update in Windows 8/8.1 will SILENTLY find the MS ones again in the background and reinstall them screwing it up.
RDP in 8/8.1 has RemoteFX added. This actually makes the RDP session noticably faster and support aero. The thing is, it is NOT backwards compatible!! The latest Windows 7 client can connect, but very few Mac/Linux clients have been updated to connect to 8, and I could find NONE that connect to 8.1 RTM. Trying every mac client updated for 8 that I could find, I managed to bluescreen my 8.1 attempting to connect, which permanently broke the ability of the XBOX 360 to connect to it. I find it humorous that I can do multi-session-per-user RDP to my Windows 7 Home Premium box with a hack that adds that feature, but could not RDP to Windows 8 Pro from my main box at work without tunneling through a Windows 7 box. Also, for some bizarre reason the new RDP only uses 250Mbps of a 1Gbps LAN connection, even for file transfers.
Some software that should work without issue in 8 and especially 8.1 refuses to install, even in compatibility mode. The only lightscribe labeler app I found that installed in 8.1RTM currently is the Simple Labeler. In this case at least it really isn't the fault of 8.1, but the stupid installers that check OS version doing an == instead of a >=, which compatibility mode isn't effective for because the installers are basically self-extracting archives that create temp files then launch them and the faked OS version won't affect the temp files.
Media Center add-in and extender compatibility has been broken so many ways in 8 and even more in 8.1 it is ridiculous. As a Media Center user, I absolutely will not be upgrading before 2020. Also, in 8.1 the guide only has 12 days of data and only indexes if Media Center is open instead of indexing in the background. In 7 it had 13 days and background indexed much more quickly, in XP 14 days.
Most currently popular disk imaging apps are not compatible with Windows 8.
While the new task manager at first looks kind of awesome, it is actually limited compared to what you have in 7. It isn't showing all processes, just processes running as you, doesn't have all the same sorting options, and doesn't let you select other columns to view. The graphs are cool, although that info is already available in "Resource Monitor" in Windows 7, its just a separate process launched from task manager performance tab and not as snazzy. Really, sysinternals process explorer is better than either of them (even with the gradual memory leaks).