I bought the 3930k to upgrade my 'Everything PC', which used to be my 'Gaming PC' until I messed up my hand and can't use 'wasd' anymore. I have been using it to try to learn what I can about virtualization technology on my own, and it is amazing what this chip can do with VirtualBox. I plan on trying to build a little network at some point in VMWare Workstation, and I have no doubt that this box will handle it smoothly.
The 3930k really is overkill. I have been keeping Asus' monitoring software up on my second monitor, out of the way, and it rarely reaches up into the 3.8GHz Turbo Boost multipliers, which means that a lot of CPU power is just going to waste. I don't at all feel like I have wasted any money, however. It means that while I don't always need the abilities of the CPU, it is capable of busting out some bitwise smackdown on anything I might ever need to throw at it. It also means that I won't have to upgrade for quite some time. I kept my Core 2 Quad Q6600 for over 4 years, and I'm convinced that this processor will be relevant for that long also.
It is certainly more than you will ever need for 'gaming'. If a person comes into the forum looking to build a gaming PC, then it makes sense to shoot them down when they want to blow all that money on the 3930k. This is because games tend to have one main thread that handles most, if not all, of the calculations related to object movement prediction and the processing of information sent from the server. They will spawn helper threads, but the helper threads tend to be very simple and rarely need anywhere near the processing power that is required of the main game thread. That means that you really only need a dual-core chip to run a game, with quad-core chips helping to make sure that other processes don't slow down the main game thread. You can get a Sandy Bridge i5 to overclock very close to as high as you can get the 3930k to overclock, so at least 3 threads are sitting there with nothing to do, and you pay quite a premium for those three threads you don't need.
If you ever bust out some serious video editing or transcoding software, then the extra threads start to pay for themselves. The same is true as soon as you decide that you want to use any kind of virtualization, because the i7-3930k supports both VT-x and VT-d (at least, now it does...make sure they didn't give you the old C1 stepping model...the new chips are C2 stepping, and they support VT-d). Having 6 cores that support HT gives you a lot of room for virtual machines.
So, tl;dr
If you want to get that chip, and you don't mind letting it run cold most of the time, then that's your business. People who are using it for nothing but gaming and Microsoft Office get laughed out of the forums, but when it comes to VMWare, you might find a good use for it.