What kind of motherboard do you have? I would be more concerned about the hard-drive being hot to the touch. Is Speedfan not picking up your hard drive temp either? Most of my hard drives are substantially cooler than the motherboard and bus temperatures. As MrCodeDude said, you will get blue screens and general instability. If it gets too bad you will see things shut down, in most cases, especially if you are lucky. In more primitive configurations it was quite easy to melt things down if you had a CPU fan stop working, for example.

Anyways, would be curious as to your motherboard, CPU and hard drive types.