I am greedy and have both
I have used the remote flash feature on a borrowed sb600 - and its great! I would need to pay a lot to get a similar feature on a canon I think.
I mainly bought my flash to use outdoors in sunlight to add some fill flash and create possibly some cooler photos. I still need practice with it though.
I forgot the sb800 came with a diffuser, its the 600 that doesn't - especially for static shots it makes for a nice shot without the harsh flash hilights.