I have a Vortex II I7 2920XM and playing 3d intensive games rarely see more than 60 degrees. Idles about 45-50.
From my experience 80 is when things get problematic (glitches and artifacts on the screen... maybe a crash).
Modern CPU's (certainly the intel ones) have good thermal controls and will shutdown (quite ungraciously) if they start to run too hot.
Also Intel cpu's now include a max heat variable that heat software can monitor too so some utilitiies now measure the heat as a reading of temperature left (or distance) from the max.