As usual, Wikipedia is the best place to start on temperaments.
I think temperament is huge and most people think it's nothing. Ah well.
My own take is that the various historical temperaments were designed for different purposes. Equal temperament (how modern keyboards are tuned more-or-less) is ideal for when you need to play in 12 keys and you can't possibly retune your instrument.
Neither condition applies to what I'm doing, so I seek out a temperament that sounds good to my ears (Werkmeister III, 'the famous one' is always good start). With Logic, it's easy to listen to a passage (the effect is especially pronounced in harmonies) in a variety of temperaments and make your own judgements. I find equal temperament to be buzzy and unsettled.