At the moment I'm playing without sets, at least until the versions become fairly stable. I usually use a good looking square ASCII set and occassionally adjust the colours. Partly to make the sense of distance and proportion more easily understood, but mainly to beautify the game. I'm a pretty visually orientated person, so using ASCII isn't out of some misplaced sense of elitism for me, but rather because I think it looks better. Until it's possible to give everything a unique tile, I don't think I will use figurative tilesets. I don't mind if a letter represents several different things, but it really bugs me if I'm supposed look at a 'tree' (or whatever tiles are used for multiple things--I can't remember) and pretend it's something else. More importantly, having a handful of things still in ascii amongst the graphical tiles really ruins it for me. It doesn't help that most graphical sets are sort of inconsistant to begin with... (they're getting better though!)
The exception to this was the tileset I remember someone showing (in a thread similar to this) that included generic heads of the various races done in a similar fashion to the existing head for the dwarves, and nothing else. It looked really good... Better track it down!