I experienced an odd problem on a Surface Pro (first edition). This happened shortly after upgrading to Windows 8.1 Update though not immediately after.
Symptom: I could connect to wifi but although I had five bars of signal strength, according to the notification area icon, I had no connection; and ipconfig reported “Media disconnected” for the wifi adapter. Tried a different wifi point, same problem. Rebooted (of course), same problem.
My next thought was another old favourite: reset tcp/ip with netsh int ip reset. Restarted, no change.
The fix I found was to go into device manager (which was not reporting any issues) and to remove the Marvell wireless network controller. Scan for hardware changes to reinstate same, and I was up and running.
The incident reminds me of how fragile Windows seems to be at times. One of the reasons I like Windows RT (the ARM version) is that its locked-down operating system should be more resilient though it is not immune (you can still scramble the registry if you feel so inclined).
Update: I may not yet be in the clear. Later in the day, wifi failed again, and this time the Marvell adapter showed in device manager with a fault icon. Enabling and disabling the device restored connectivity. A driver issue with the latest Windows update? Or failing hardware?
That is one thing I have found with Windows 8/8.1 though, it seems even more inclined to randomly fail with Bluetooth and WiFi for no apparent reason. If anything Bluetooth seems worse on 8.1, I have one device I always have to unpair and pair again when I want to use it as it never connects otherwise. It initially worked fine on the same device before I upgraded to 8.1.
Then again, my Galaxy Note 3 has awful WiFi problems on 5Ghz and sometimes even on 2.4Ghz, on networks that work perfectly fine on other devices. So locked down certainly does not always equal stability.
I have a Surface Pro 2 and it exhibited the same WiFi problems within a week of delivery. Perhaps I should have returned it, but after spending ages configuring it just how I wanted, I hung on. Following nearly six months continual heavy use there have been about three episodes, all resolved in straightforward manner by disabling/reenabling the Marvell device as you describe, Tim. The thought that it might be dodgy hardware, waiting for fail completely, was the only thing that gave me any worry with an otherwise superbly engineered and brilliantly performing machine. But it seems like ages since the last glitch. Until reading this column I had pretty much forgotten about it, thinking that any of the regular stream of firmware updates mustt have nailed it.