I also put both both Windows 8 and Windows To Go through the entire suite of PCMark 7 tests. PCMark is a popular benchmark designed to measure overall system performance (CPU, hard disk, graphics) by simulating real-world scenarios such as browsing websites, copying/pasting huge amounts of text, rendering video files, gaming, scanning for viruses, etc.
I repeated these tests several times and the results were the same: I lost quite a bit of performance (nearly 300 points) most likely due to the fact that the USB 3.0 drive didn't achieve the same throughput as the built-in SSD of the Core i5 Samsung tablet I used for testing.
Overall, the performance differences were negligble and barely noticeable in day-to-day usage.
Disk space becomes a luxury item
With my review unit being just a 32 GB thumb drive, I instantly noticed where Windows To Go quickly hits its limits: Having installed all my most critical applications, I was left with about 8 GB of free space. I'm not sure how much of an issue this will be for enterprise users, since Windows To Go is designed for scenarios in which users won't be handling massive amounts of data (you won't hand your CFO or Creative Director a Windows To Go stick and tell him to scrap his desktop). Also, as I mentioned earlier, SkyDrive makes up for a lot of that shortfall in storage space. I went with the 125 GB option and didn't miss the local storage as much thanks to my 100 Mbps connection (I guess I'd quickly change my mind if I had sub-10 Mbps speeds).
Bottom line: My "emergency" Windows 8
Overall, I came away impressed: Windows To Go offers the entire Windows 8 functionalty on a handy USB thumb drive. This should make things easier for any IT pro who would rather carry a USB stick than a laptop. What I don't understand is why Microsoft hasn't talked licensing yet and why this feature is strictly enterprise. I assume Microsoft will open up Windows To Go for a broader audience sometime in the future. Until then I can only advise admins to take a look and evaluate how Windows To Go could ease some of their BYOD (bring your own device) pains.