I'd like to add my thanks to Khue. After having performed a successful app push for the first time today I'd like to add a couple of observations:
1. A reset of the target device (remove battery & SIM) "appeared" to kick-start the app install. This is unconfirmed at the time of writing and needs some more testing.
2. I was unclear as to whether the Handheld Configuration tool needed to be run on the BES - it doesn't. Setting up the software configuration and policy worked from an administrative workstation.