Idk but i suspect something to make the path to 2.1 smooth. I have read many people getting this 1mb update on many different build numbers. As for myself i have two PlayBooks, one sitting on 2.1.0.840 and one sitting on 2.1.0.560 and neither have gotten the 1mb update.
some users are reporting a new bug report app while others see nothing new. As i said i suspect its something to make the upgrade path to 2.1 smooth.
Got the 1MB update myself this morning. The message about it popped up as soon as my Playbook booted up. I am on the latest 2.0.1 beta, which I only downloaded last weekend.
I installed this update this evening. I did have to restart my Playbook, but there was nothing to report as far as changes go. Though it gives me hope that the release for 2.1 isn't actually going to be too far off. Farther than many hope, to be sure, but not super far away.