From a performance perspective, you don't want to under or over inflate tyres. Nice item by Tom Anhalt:
http://www.slowtwitch.com/Tech/What_s_i ... _1034.html" onclick="window.open(this.href);return false;
One quick “takeaway” from the above plot is that if one hasn't identified the "optimal" pressure for their particular setup, then it is far better to "err" on the side of too little pressure, than to "err" on the side of too much!
A good starting point for tire pressures is to follow the recommendations of the tire manufacturers. Most will give both a recommended pressure that's less than the maximum pressure, and some give fairly detailed recommendations based on rider weight and conditions.
Add to that there are certain circumstances where you don't want too high a pressure in order to improve handling, think crits, and also wet surfaces.
As for safety and heat factoring in blowouts, it's definitely a problem on road bikes on long descents with frequent heavy braking requirements. The sidewalls/beading becomes more easily removed from the rim. e.g. if you have a clincher tyre-rim combo that's hard to get on/remove on a cold day, then simply warming up the tyre can help make the job easier. And if your tyre-rim combo is pretty easy to remove by hand, then keep that in mind as pressures build.
Heat blowouts are even a problem for tubulars. Anyone who's raced at an outdoor track meet in an Australian summer will probably have heard that unmistakeable gunshot sound of someone's tyre blowing out while the bike is on the rack sitting in the sun.