The 1.0 series is not binary compatible with the 0.5 series and is currently in active development.
The 0.5 series is stable API and ABI frozen and in bug-fix only mode. It's shipped with Ubuntu 11.04 and 11.10.
Development of the 0.4 ABI series
New Maverick series
Maverick development series
Saucy Salamander support series (13.10)