Sadly if one is looking for a universal source of clean and cheap energy, geothermal sources are still quite a long way away. That is not to say that these problems cannot be overcome. Engineers are good at performing miracles, after all. Hell, even the impossible can be achieved with time and money as the Sovs proved. But therein lies the true problem. The Russians took ten years and God knows how much money to sink one hole. A viable geothermal station would probably need several tens of holes. At current prices and with current technology the cost of establishing sufficient heat mines to make this concept practical are just too great to make it commercially viable.
Do go and read the whole post: I found it quite fascinating.