[Someone]

"OS X handles some of this by assigning mnemonics to keyboard trademark symbol ® is just option+r. ∑ is option-w."

And, after they ran out of mnemonics, they sprinkled the rest of the characters on the keyboard (almost; I think they tried hard to keep things memorable, but some combinations are just plain of the "if you don't know it, you 'll never guess". The Apple logo is on the k key, for instance (IIRC). Mnemonic? MaKintosh?)

"Diacritics are two-stroke combinations, to get é, you'd type option-e, which puts the ´ on the screen, and then type the e to complete the character."

That's the old way. Recent OS X has 'hold down the e key, a menu pops up, click the desired variant or type the digit shown next to it'.

[Karunamon]

Ah neat, I wasn't aware of this. Every mac I use has the press-and-hold mechanic disabled to support a higher repeat rate. I might have to go back and play with it some more.