Currently I do developing my own Roaming VoIP PBX as a Rasbbrry Pi image, and have to rebuild project packages often. It is not best idea to compile packages right on Raspberry Pi. That would take hours. I was searching for a tool that can create image base — on my laptop or VPS.
Here is good starting point: http://blog.kmp.or.at/2012/05/build-your-own-raspberry-pi-image/, there is an shell script that will build image (right-click and select ‘download as’).
Some links about cross compilation and QEMU (QEMU for emulation and compilation on “Raspberry Pi” environment):