I have been waiting for this since the late 90s! Absolutely essential for academic and serious archiving work. It produces a single file, the file is indexable, it adds source/date metadata, it edits/annotates, it saves selectable sections and links, it autosaves, there is a version for all major browsers, the saved file opens in any browser without the need for an addon so it's browser agnostic and future-proof, and more. The only thing missing (I think) is being able to edit/annotate the previously saved file. Brilliant and should come as standard in all browsers.

EDIT: Actually, you can edit/annotate previously saved files and SingleFIle cleverly won't touch the info bar if there is one already. Excellent! 6* for that. Now I wish you could select first and then click on the highlight button rather than the other way round :)