Posted by Notch on April 27, 2011 (Super late right?), Notch blogged about what his plans were for Beta 1.6. He said they were going to "mostly be bug fixes". That's a good thing, I mean look how long the freking bug list is, I mean jeez.
But alongside those bug fixes are two new features. One is the addition of an officio Nether world inside SMP servers. (Confirmed in his blog post on May 2, 2011). But the other thing an ingame map. It's a craftable item (Paper + ???) that allows you to zoom in and out to display the land around you. The map auto fills out as you explore. If you go outside the edge of the map, it will stop updating, causing you to make another. Now for screenshots.
Fully Zoomed In
Fully Zoomed Out
You can drop your map in SMP and another player can pick it up, seeing your progress. Apparently theres a limit to 65,536 per map, but that doesn't seem like a problem.
Keep in mind this is basically a re-blog of Notchs blog post, posted in a shortened version. Find his blog here, at http://notch.tumblr.com/