Simple sidebar, hideable, 'cloud'-synched place to scribble down notes to yourself while browsing. Love it!
I've been using it for over a year now and it is so much nicer than having to open up notepad just to copy and paste bits of text or notes to myself while browsing. (I used QuickNotes long ago, but those are specific to a single browser/computer, whereas these are right to hand anywhere).
I can see wanting added features (tags or categories), but I'm not sure that wouldn't just burden it down, frankly.
[I do wish it wouldn't so often need me to open up options and click "login" (next to the already filled-in information) for it to start working for the day. But it's a minor nuisance, given how ridiculously handy this simple add-on is.]