It was bugging me that on Facebook, if I typed something like -20°F, the 
line might wrap between the minus and the 20.  Then I read in Wikipedia 
that there is a minus sign, different from the hyphen:

http://en.wikipedia.org/wiki/Plus_and_minus_signs#Minus_sign

Copying/pasting that solved my problem, but that created the new problem 
that I want to be able to type the minus without having to go to Wikipedia 
to copy/paste it.

That's when I found out that I can type any UTF character by first hitting 
ctrl-shift-u, then typing the number, then hitting space.  The minus is 
#2212, so this does the trick:

ctrl-shift-u
2212
space

Alternatively, I can hold down the ctrl-shift while typing the numbers, 
instead of releasing after the u, and then the UTF character appears when 
I release ctrl-shift and I don't have to hit the space.

That doesn't work in every program, though.  It worked in my browsers on 
Ubuntu, but I don't even know if it works outside of Ubuntu.  I don't know 
how to use it in Emacs.

There are UTF characters for °C (#2103) and °F (#2109):

−40 ℃ = −40 ℉

They don't look so great in some fonts, though.

Anyway, I thought some of you would be interested in that trick.  I hadn't 
heard of it before, but I could be the last one.  ;-)

Mike