It’s called WikiStat and shows the time distribution of up to 250 of the most recent edits on an article, giving you a quick insight on how recently and intensively edited a page has been edited.
I haven’t tested it with anything other than GM 0.7 and FF3b3. I do recall that Opera can do user scripts these days, so it might be able to do it too. No promises though.
I’m most interested in suggestions for improvements.
Added a pie chart to show approximately how many of the edits were reversions. Makes for somewhat depressing viewing when you then consider there’s an invisible but equally large and ultimately non-productive segment of the pie.