I too lost my P2 and gopro over the ocean this morning. I'm right now visiting the north shore of Kauai and have flown over the ocean several times in the past few days with no incidents. Last night I upgraded the firmware to 3.06. Early this morning I sent the quad up a couple of times over the ocean bluff here. The first time it came back no problem. There was about 50% of battery left when I sent it up a second time, and expected to be in the air less than 5 minutes. Just when I was ready to return back, the sticks stopped responding altogether and I noticed that the bird was dropping lower and lower. I tried shutting off the controller and waited for auto return home to kick in but the P2 kept descending. It didn't return home first, it just started dropping from it's position. It landed in a cove but am not really sure where it landed there - it could have been in thick vegetation or in the water - my view was blocked as it was dropping. We've got a search and rescue party set up for tomorrow morning to find it (seriously).
I also noticed the throttle wasn't as responsive but at first wasn't so concerned but now I know why.
After the firmware update I did all the normal stuff like making sure I calibrated the stick using RC Assistant, then calibrated the IMU and sticks from DJI Phantom 2 Assistant. Of course did compass calibration on lift-off.
I doubt there is anything I missed but I wish I was still on the previous firmware level.