After about a month of searching the internet and chats direct with Intel, I have come to the conclusion that the 2600k internal graphics (Intel HD 3000) are flawed and I personally through my company will not be using this configuration and I recommend others do the same.
Recently, I have purchased a few systems with a combination of H67 boards and I3-2120/i7-2600k processors.
All the 2120's have been completely flawless, however I wish I could say the same with the 2600k systems.
On the boards I have tested it on (Mainly Asrock H67DE3, but also a few others), I have seen random hangs and crashes (Started thread on Intel Forums), the default drivers from manufacturer and Intel direct fail, with some making the machine pretty unusable.
For all my clients with I7-2600k systems, I have purchased discrete graphics cards and this has beaten the problem.
I am still not 100% sure if it is a(nother) chipset/board issue or simply a driver issue, but my experience tells me that this is most likely down to drivers.
Looking on the Intel Support forums and just searching around trying to beat this problem has shown me that many other people are having similar issues. As for why it is not more mainstream/reported elsewhere, my guess is simply that as the I7-2600k is a high end chip, the vast majority of people with it are using p67/other boards along with discrete graphics cards.
The Intel HD Graphics 3000 are powerful (when working) and an equivalent discrete card costs in the region of £40-£50, along with the additional power draw (around 15w idle - 60w+ peak), meaning that the processor is very good value for people wanting raw horsepower but are not big gamers.
As for buying advice, for my clients I am switching to the I7-2600 (non K) and am still using the H67 boards with discrete graphics since the reason for getting the K variant was the 3000 instead of 2000 graphics as overclocking is not high on the priority list.... If you have people wanting to overclock, the 2600k + p67 + discrete graphics is safe.