I have been reading a ton of the forum threads on the Jagger update. Honestly, the best stuff is still at WebmasterWorld, IMO, on this particular update. This weekend, I read most of the Update Jagger - Part 2 which described mostly two things;
(1) Duplicate content issues due to www. vs. non www. or /index.html or / or not and so on. Mostly canonicals issues, affecting page rankings in this update. (2) Reciprocal linking, seems to have been spotted and discounted.
Now, at the same time, people in these threads are reporting the direct opposite results. So it is hard to no for sure, without doing my own tests - which I haven't done - nor will I until this update is over.
Jagger 3 is on its way, Matt Cutts explains that Jagger3 was visible at the 18.104.22.168 data center since November 4th. It seems some of the canonicals issues have been resolved with this Jagger 3 update, but it may be too early to say.
WebmasterWorld has a huge thread already on Part 3 of the Update Jagger. Mcdar built a nice tool to keep track of this Jagger update at http://www.mcdar.net/jaggerresults.htm. Reseller in the thread writes;
We can assume that the following DCs are showing at present Jagger3 Beta-2
While previously the following DCs had shown Jagger3 Beta-1 ;-)
22.214.171.124 126.96.36.199 188.8.131.52
So lets watch these threads and our own results and see what Jagger 3 gives us.