Is it all strictly online? If it also works offline on the client, how does it deal with synchronizing multiple "timelines" created by copying the saved file?
They don't display it as a tree, but it's logically identical -- just flattened out into a list form with the inactive branches grayed out.
They say "With our new Time-Slider, you can browse the complete history of a document using a familiar user interface." (emphasis mine) It says nothing about editing.
But it seem unlikely the edits you did last week between revision 2.3 and revision 2.4 would especially interesting to look at. Perhaps yesterday's edits would useful...
What I would like would be an editor which would go-back only on a given selection (cutting and pasting would make implementing such a feature hard but git because clever things...).
but not for hacks writing web content or your mother writing an email.
I was doing some research for a paper on fine-grained version control to be able to deal with web content, recipes, songs, and other types of "documents" which rely on things other than paragraphs and lines. There has been a LOT of research done on the subject and I found some papers that deal with version control for Web content and some for dealing with XML content.