There's lots of threads about this, but I could never find the ASA side of the configuration.
This is the configuration I have working, for both the ASA and the Playbook.
IPSec is tough to get right, and if the ASA is not set up right the VPN will fail through no fault of the playbook.
Set this up, get the new RDP client, and enjoy some remote access goodness :D
Blackberry Playbook to Cisco ASA VPN - Robert's Blog