I'd love to hear from someone who prefers unweighted.
I prefer unweighted. I currently own a weighted keyboard but find that playing it is not as much fun as playing the semi-weighted and unweighted that I use in church because of the strain on my hands. This might be because when I was first learning piano all I had was an unweighted keyboard to practice on and I only used weighted during lessons. I had no problems playing on weighted keys, however. I would consider myself a keyboardist (if that term even exists) rather than a pianist if I had to identify with an instrument. If I were to invest in a more expensive synth/workstation/arranger, I would probably buy a semi or unweighted version and keep my current keyboard to use as a controller for it in case I really wanted to play weighted.
When it comes to dynamics, I noticed a difference coming from the deep, semi-weighted keybed of the Tyros series to a noticeably shallower, unweighted keybed of the PSR keyboards. I believe this was mostly because the Tyros keyboard is deeper and hence provides a greater range rather than providing more resistance. That might be an illusion, however.
One more thing I noticed is that the less experienced wannabe-musicians (like myself) actually tend to prefer unweighted keyboards, though this is probably an over-generalisation. To start with, when I first played Tyros, I didn't like the keybed at all. As I gained experience, I began to like it a lot. I also noticed that some teens that I know who can hardly play dislike the Tyros action and prefer the PSR. I might come to like weighted keys. Who knows.
I don't know if I am the right person to answer this, as I do not consider myself a musician and I am not trained. Hope I provided some insight though.