I have to say that I really like this service. I used to use del.icio.us and time after time I had no access to my bookmarks because of heavy traffic so they say on my internet service provider. Since I could access everything else - and I have cable internet - it didnt make any sense so I changed and I am very very happy with my new diigo service. I hope that I get to participate in future improvements with this service.
I recommend to put the first two icons beside the adress bar and hide the Diigo bar. You can access to the most relevant features from there and you'll get more space for websites:
I have tried the Google Toolbat, the Advanced Browser Toolbar, and even fell as low as testing out Microsoft's Windows Live Toolbar. But this one hits the spot :D
The toolbar works beautifully with Flock, and I'm using the 2.0 beta release. You can set it to "Icons Only" and then move them all up next to the icons in the Flock Toolbar, literally extending the functionality without losing any of the form. You have to move the icons individually, which is a bit of a pain, but the result is sweet!