If you are a Second Life user, you might want to cast a vote for fixing a problem occurring in Second Life apparently since the upgrade to the Havok 4 physics system.
The problem is that hovering avatars are sinking.
The description is as follows:
Turn left or right (the avatar, not the camera controls). The simulator will start to slowly move you down.”
If you are an SL user and would like to vote for getting this fixed go to https://jira.secondlife.com/browse/SVC-2013 .