After some debate in my head, I took the plunge when building my new DAW pc to go with W8 Pro rather than W7. Despite the (predictable) push back from some quaters regarding the 'Modern UI', nee Metro, I figured the benefits were worth the risk. I'm very happy to say that so far the process has been silky smooth. About an hour to get my head around the new UI, but I've resisted downloading the W7 start menu add-on (you really don't need this even in the Desktop mode). A minor issue with a Netgear Wireless NIC (drivers install but the device isn't picked up at all, so I used another brand), a CD-ROM that wasn't working due to the power cable not being attached properly which also required a visit to the BIOS to re-enable it - and that was it!
X2 installed with no problems (I included the quick patch as well as X2a), and once I'd found the genuine W8 drivers for my SPS25 audio interface that too was no problem. It does seem that W8 is picky about hardware drivers - you need to ensure that you have W8 drivers - neither W7 or Vista drivers worked at all for that device. Omnisphere loaded without any hitch, as did DimPro and Rapture. I've yet to try EZ Drummer and other 3rd party VSTs.
The new PC has a lot more power and memory so as expected runs quicker anyway, but overall I'm very impressed. For those in two minds - if you can source the appropriate W8 drivers I'd recommend it as the way to go.