I like the fact that you don't need to sign in with the bookmarklet (contrasted with instapaper).
The incredibly clean interface is another draw for me. A lot of these other sites are all "web 2.0"ish and to me it's bothersome.
I don't really like the chromium extension. I dunno, I think it's kinda useless seeing as though it's off to the side, whereas the bookmarklet is right on top of what I'm viewing. Also I like the notification window of the bookmarklet better than the extension. The window when a "page has already been indexed" on the extension is a bit annoying. I'd like to see maybe a keyboard shortcut for the extension, I think that would make it killer.
A couple things that I would like would be to search through a time range, also better browser integration would be nice. i.e. having pages show up under the autocomplete. The ability to select multiple items would be nice. Having a text only view (a la instapaper, readability). Also I wish there was a shorter url, I always spell historious wrong.
thanks!