See I still use del.icio.us and here is why. Now my compatriot has been telling me how cool simpy is, but I have so much already invested in del.icio.us and frankly now that it has even tigher integration into firefox I am less likely to change. I mean its got handy buttons (See Fig 1)
and lets you take notes (See Fig 2) by highlighting portions of the current viewed page.

del.icio.us buttons
Fig 1

del.icio.us notes
Fig 2

I will be using it for the next week or so and write a more formal review then, in the meantime if you use del.icio.us check it out.