Google AdSense has an ad unit known as a link units, which are simple text based links that are ads that drive you to a page of ads. Normally, on the vertical display you get a maximum of 3 link units but some publishers are saying they are seeing 4 or more.

Here is what Google shows as an example:

A WebmasterWorld thread has some AdSense publishers saying they saw more than just the 2 or 3 links in this vertical ad links unit.

Here are some comments from the thread:

Have you seen more ads showing in your ad links units?

Forum discussion at WebmasterWorld.