What's in this version:6.4 addresses device stability issues introduced with the 6.3 for certain set of HTC and Samsung devices.
New Image Gallery option for photos from SmartFilter (phone version)
Zip It now can zip retweets of a user or a tweet source (e.g. hide Foursquare check-in tweets)
New features on tablets - Search Party and My Stats
Find friends using similar users from anyone's profile
imgur photo preview support
Read Later with Readability
Facebook sign-on and posting improvements