As a student spending the semester in Madrid, I got a first-hand experience with all the
different types of toilets found in Spain. 
Overall I would rate the toilets as usuable -- but not much fun. Although they are clean in some places (make sure to go only in good establishments), the Spanish seem to forget such necessities as toilet paper or soap. Also, like any other big city, a lot of people (probably 2/3rds of them) neglect to wash their hands -- although if you were to ask a Spaniard, they would deny every word of it.
There are four different types of Spanish toilets: Note of interest: dogs are everywhere in Spain, yet there are very few designated bathroom spots for
them. Make sure when you are walking to watch the ground or within a few minutes, your feet will be
brown. Also, wear waterproof shoes.
-- Suzy [2]
Type 1: The Dirty Hole in the Ground With Marks Where to Put Your Feet. Usually found in
tiny towns with two or less main streets. Just squat and fire.
Type 2: The Big City Toilet. The big city toilets are a lot like toilets in any other
major European city. They usually don't have levers to push, but instead have pull flushes or flush and stop
buttons. The pull flusher is the lever on the top of the toilet that you pull up. But be careful, if you hold it
up for too long, it will overflow. Or, if you pull and immediately let go, it won't flush everything. If
everything does not go down at once, you have to wait about 2 minutes for everything to go back to normal, and
then you can flush again. Make sure to wait those 2 minutes or everything will overflow.
The toilets are usually not very clean, as the Spanish don't seem to know how to flush real well.
I guess they haven't had enough practice using them. Make sure to wipe the rims before you go, as many
people have not had much practice aiming, either.
Type 3: Bidets. 
[1] In hotels and houses, you will always encounter one of these, accompanied by a small
towel. Make sure to use it after going to them bathroom, as it is considered unsatitary not to use
one. Helpful hint: learn how to use a bidet and what they are for BEFORE coming to Spain, as the
directions are not posted on the walls.
Type 4: The Metro. Up until about 20-30 years ago, Franco ruled Spain and the Spanish were not allowed
to show pubilc affection or talk about the government. Basically, the Spanish weren't allowed to do anything.
Since Franco's death, Spain has become a very "free" country. Now the metro system is used as a place for
everything -- sex shops, make out spots, a city-wide bathroom... just be careful where you are walking or sitting.