While excess heat isn't good, it's not too much of a danger.
There is a risk of the computer crashing if the heat gets too high, and it may make the computer slower, but otherwise, it's no big deal; I speak from experience with a rather low-spec laptop, and it's own overheating problems. The only problems were the afore-mentioned hysteria-crashing, and my left thigh, which is now quite heat resistant, at the possible cost of scarring.