The two major changes according to AdSense include:
(1) Google now requires AdSense publishers to comply with “the spirit” of the AdWords Page Quality Guidelines. (2) You can place up to three link units on a page.
I took a deeper look and compared the old version with the new version.
The new version added this line:
Publishers using online advertising to drive traffic to pages showing Google ads must comply with the spirit of Google’s Landing Page Quality Guidelines. For instance, if you advertise for sites participating in the AdSense program, the advertising should not be deceptive to users.
And in regards to the link units, the old copy was:
A single link unit may also be placed on each page.
And it now reads:
Up to three link units may also be placed on each page.