Ben Wilkie said:If you can afford it, get it.
Fretless bass is a wonderful sound, but it's worth getting someone who knows what they're doing to have a look at the bass, do a setup, and make sure your strings are appropriate for what you're trying to achieve. I mucked around on a fretless for months trying to work out why I wasn't getting a Jaco 'mwah' - turns out the strings were too dull and too high, and I was getting more of a flatwound thump than anything.
Anyway, fretless can add something special to a lot of tunes, especially ballads (for some reason I've got that Dream Theatre track in my head) and acoustic tracks (think Joni Mitchell). Also great for bouncy walking bass and stuff. And, of course, solo work.
Check out Gary Willis, Tony Franklin, Jaco's work with Joni Mitchell (IMO his best playing), and for something different check out Juan Alderete of The Mars Volta - his playing on 'The Widow' really stands out.
I agree on the set up.....that is key!
The set up protocol is very different.....you need a luthier who knows this
I totally agree on the ballad comment.....I used my mwah on the slow or melodic songs more than on the rocking stuff.....when I play a fretless on a rocker I make it sound more like a fretted bass
Fretless basses have their place....in my opinion it all comes down to funding for you at this point