Norbert Hoeller wrote:

Although MediaWiki has a good history facility, it would be great if the text in a page were flagged to indicate changes since the last time that page was viewed. This could range from revision bars in the margin to marking adds/changes/deletes similar to Word change tracking. Are old versions of a page saved by MediaWiki or are only the changes recorded for the revision history? Also, does MediaWiki record (a) when a user last logged in or (b) when a user last viewed a page? Thanks, Norbert

There's an advanced watchlist feature which you might use. You get on the history page "updated since my last visit" next to those revisions (you must see the history page before the article page). You could then diff them. Mediawiki doesn't currently have in.text diffing. You can only see the changes on the mediawiki source, not on the shown text, so it's not too friendly for reading.