The Intel P4 standard heatsink and fan are pretty easy to put on, but a royal pain in the butt to take off.
Heatsinks are a pain because of a couple of issues.
1. They need to be tight and firm against the CPU in order for a heatsink to work correctly.
2. You have to put them on straight and stead force. I have seen many AMD chips that are cracked due to incorrect methods of putting on a heatsink.
3. Due to smaller chips and more devices on a mobo, there is little or no space to put on a heatsink and fan in the first place.
Remember back to the 386 and 486 and even the P-I when heatsinks weren't even used? I use to use a P-I 133MHz and overclock the hell out of it and crack up the voltage to get 200MHz out of that little chip with only a heatsink, no fan. And the heatsink was 6 pennies I superglued together. Now those were the days.