I've used Identity columns a lot in my data warehouse work, and I love the simplicity they bring. I've also used them extensively when working on transactional systems, and again found that the simplicity made for easier modelling.

However, more recently I created a new system and decided to go for entirely natural keys. For no other reason than I fancied a change to what it was like, and so I ended up with natural, composite keys that brought a certain elegance to the design.

I'd say it was more work with the natural keys though. And if I was building the same system again, I'm not sure which way I'd go.