I've not seen anyone provide much of a summary of the Jagger changes. I'll cut all the interesting bits out of a summary I produced for a client and offer up bare bullet points here.
- Anti-spam improvements: Google’s sought to reduce the number of spammy sites in search results by formulating more thorough and more accurate automated means of spotting hidden text (text hidden in layers was particularly targeted). Google also improved its ability to spot doorway pages (pages fill of keywords which serve no other purpose than to link to another page, often on a different domain).
- PageRank update: The PageRank metre on the Google toolbar was updated.
- Links update: The number of backlinks shown by the “link:” search command was updated.
- Changes to Chinese and European search results: Google tweaked its geographical filtering. Most of the sites we work with and which are hosted in
Europesaw fairly substantial gains on Google’s .com results. This suggests that the weight against sites hosted outside the was reduced. Google now has more faith in other algorithmic means to determine a web site’s target audience. US
- In this period we saw high traffic sites which have been online for four or more years improve their search results over than younger or lower traffic sites.
- Ranking algorithm change – deep links increase in importance: Links from external web sites to pages beyond your home page are now important. In this time new monitor stations gained PageRank 1 or 2 on their home page and those we test with deep links earned PageRank 4 or 5 on their popular deep linked pages.
- Ranking algorithm change – keywords in domain names: Having a keyword rich domain name became more beneficial as the weight against keywords in domains was reduced.
- Ranking algorithm change – hyphens in domain names: The weight against multiple hyphens in domain names increased.
- Ranking algorithm change – measured traffic: Google has an idea of the traffic a web site has by monitoring click throughs from Google’s own search results and through users with the Google toolbar and other Google software. Pages (not sites) with particularly low internal traffic (from users already on the site) dropped in rankings in favour of pages which users visit and find more often.
- The Jagger2 update included the results of the first sweep of spam reports which followed Jagger1.
- Index change – Canonical corrections: Google improved its understanding of which is the most appropriate URL for any given web page and when two or more URLs may actually refer to a single site (for example, http://example.com or http://www.example.com).
- Ranking algorithm change – Freshness: Google changed the importance of a page being either fresh or stale. Certain keyword searches suit fresh pages more than stale pages (based on user behaviour) while other searches favour stale (not recently changed and old) pages over fresher (recently changed or added) pages.