I started to use diigo two days ago and I'm absolutely into it. Replaced my delicious right away (which I used for 5 years frequently!).
Suggestion 1: Nice thing to have would be a snapshot-feature which snapshots the website's layout as well.
Suggestion 2: what about enterprise plans with support, trainings or maybe special features (like suggestion 1). I use some platforms for professional knowledge management and collaboration and think that diigo would be predestinated to offer such features (SSL, Storage, encrypted storage...).