RE: XPS 15 fan, on/off/on/off, gahhh!!!
I've had my L502X since summer 2011. It's in heavy usage as I take it to and from work as well as have it in use after work. It's my everything computer; 5 years and still kicking. I've done my fair share of maintenance on it, which is what helps keep it going.
I could go on forever about little things I've had to do, like replace the subwoofer 2 times, keyboard 3 times, etc.
The main thing I have to do to keep the fan from going into "ON/OFF/ON/OFF drive you crazy mode", is tear down the laptop and clean out the dust blocking the exhaust fan. My temp is at 60C right now on an i7 cpu with a room temp of 25C. I can tell when I need to do a tear down, it's quite hard to not notice or drive you crazy. Imagine someone with a hair dryer beside you and turning it ON & OFF for hours. It's like water torture. I've gotten my tear down to 15 minutes, as you know you basically have to take out every screw to get to the CPU among other components as well. The tear down and clean out is the only thing that temporarily solves this.
Now I did pay Dell for their extended warranty service a few years ago and they sent a technician to my office and he replaced the whole heatsink and put a new fan in. Once it got clogged with dust, back to the ON/OFF pattern again.
In my 5 years, I would say 90C+ is normal for this laptop while gaming and unclogged of any dust and 60C is normal for idle.
I would also add that this laptop would be in the garbage if I wasn't an IT geek. For a normal person this laptop would have been pronounced dead and in the garbage by now.