http://googlereader.blogspot.com/2010/09/turning-off-track-changes-feature.html

<<As of September 30th, we’ll be turning off track changes in Reader. While this isn’t a widely used feature, we wanted to let you know in advance so you can set up a suitable alternative (such as http://page2rss.com). Your previous updates will not go away, but you will stop receiving new updates from any custom feeds you have set up.

We apologize for any inconvenience this causes – and as always, please feel free to visit our help forum if you have any questions.>>

Never used it :-)

Damned I will have to list all my feeds using this tracker in order to remplace them