As well was the main documented features of Android Honeycomb 3.1 which can be found here, there are also many 'hidden changes. If you spot any post them here.

Browser:
Google Instant available in labs

Gallery:
New crop interface when setting a wallpaper
Picasa albums can be 'pinned'/made available offline

Google Talk
New Emotion pictures in chat

Market:
Applications now show as being installed when browsing
Now remembers position when searching through apps

System:
Different colour text selector handle
Long-press accessibility options
Upload/Download Indicators on the WiFi status icon
If you have your Xoom 3g in Airplane mode with wifi on it remembers after reboot.
When you click System Updates, you can now click, 'Check now' for updates
New Debug icon in notification area

YouTube
Playback controls are now along the bottom and can be used while buffering
HQ option now renamed to HD

via