Having just got Tiger... I just found this one out thanks to this post. What a fantastic feature! So now if someone is having a go at me in a post and using big words, I'll know what they're saying.
There are so many features in Tiger that are brilliant. The jump from Panther to Tiger is the best jump so far.
Camino has two parts: An all-aqua new system, and an older drawing system, Gecko, that is based on Netscape Navigator. Once they finish overhauling Gecko, they claim that Camino will rock dictionary support.