For a Mac Pro, the procedure is:
1) Flip lever on back of case. Side panel hinges out smoothly and effortlessly.
2) Slide memory board out by grabbing the two finger holes on either side of the board.
3) Snap in DIMM modules, slide memory board back in
4) Replace cover. Start machine.
Zero tools. Zero configuration. AFAIK you can even put the DIMM(s) in any open slot. Now that I know the procedure, I bet I could do it in under 30 seconds.
It was just surprising to me. Most PC's, even the nicest ones, have screws to be delt with... or wiring harnesses to be worked-around... or cases that don't come together perfectly... it's always something.