I was just noodling over something similar the other day with regard to the "speech-to-text" bit. I know that when you speed videos up on Youtube, the audio speeds up as well. I always wondered if the speech-to-text algorithms were able to transcribe that. My first thought was "the NSA can probably do this".
While I don't have a specific solution in mind, I just came here to toss ideas around that I think could be part of one. It would be cool if there were a "bookmarks dashboard" that tracked when you set the bookmark and then other metrics like the last time you visited. It could also be useful for looking at the content of the bookmark, comparing it to other bookmarks and suggesting groups/categories. Other thoughts: tagging, sharing, comments, etc. Also, the ability to notify you when a bookmarked page has been updated (via dashboard, desktop notification or rolled up into a weekly newsletter of some sort).