In the early days, Delicious and Reddit were often talked about as being in the "social bookmarking" space since they both centered around sharing links with other people. Remember Reddit didn't even have comments for a long time! The distinction was in Delicious you tagged links, in Reddit you voted on links. I visited both regularly to get my social link fix.
I'm sure from your POV Reddit has always been an entirely different beast, but (and at the risk of teaching my grandmother how to suck eggs) as an early user of both I saw them as have a lot of similarity, both forging a similar and exciting new future of people collectively making the web more discoverable.
I actually tried to build a product which attempted to combine the best of both: a tool for communities to organize links. I still think there is room for something like that, but countless people have tried and none have taken off, so it seem it is way harder to get something like that to catch on than it seemed in those heady days of web 2.0.
You misremember. Digg said it was "social bookmarking" for a while which caused me no end of headache, but Reddit never did and I don't remember anyone ever talking about them in that context.
Neither Reddit nor Digg offered actual bookmarking, so if you thought they were similar to Delicious you didn't really understand the product.
