I thought it might be because, primarily, I use Safari to browse on my mac at home and Google’s Chrome in the office for social stuff. This means I don’t really take advantage of the nice Firefox toolbar or other browser integration.
Then I thought again and actually what stops me using it as often as the others is the submission process. With Delicious and Reddit the process feels very much “click,click, click, done”; whereas with Digg it feels far more hit and hope that the title and description will appear and that I won’t lose patience before I get to the final step.
So the answer to that rhetorical question is “sometimes not”. Or to be more specific, sometimes I just can be bothered.