Temperature in server room. How hot is too hot?

To keep an average room 15'X15' at ambient 68-75F, for every 300 watts of system power a minimum of 1000BTU/Hr air conditioning would be required. In agreement with leew, anything over 75 is pushing your luck.
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I just looked at a couple of dell specs and the operating temps were 65-95F  so the news is that's the temps you should run at. Of course this is a professional driver on a closed course so your milage may vary.  I have never found a PC/Computer that couldn't operate at 85F now that's a pretty warm room.  The major concern is not so much the temp of the room but what is the variance of the temp in the room,  If the temp swings any significant amount (15 to 20 degrees F) that would be more harmful to the machines than a constant high temp.  

jimmyd - you run your server room at 85-95 even 80-95 for weeks or months on end and see how much more system failures you have.  Internally - that is in the case - the temps are often upwards of 80+ even 90+ degrees.  Keeping the room temp helps keep the internal temps cool.  I've seen machines die when server rooms hit 90.

For the servers, the warmest room I have (using a 24hr charting temp/humidity monitor) is 80F with 70% humidity it's run that way for several years and only had two machine failures (same brand and model power supply dramatically failed causing the loss of the motherboard) and one hard drive failure, of course saying that I've jinxed it and we'll have another failure next week. The other roms normally run around 72F, But I do have some workstations that are in 75-85F environments the failure rates are a lttle higher than the servers but I believe the problem is the temp swing not the temps themselves, and the constant cycling power off-on.   What I was pointing out is to look at the specs of the machines you use, all vendors publish the operating tempature and most even have a storage tempature rating.  follow the manufacturer guidance, but that sould be true for all aspects of operation.