It would be very nice to have a document that explains how to support a new platform, both sw (and by that I mean porting the whole system to an Ubuntu-based distribution, for instance) and hw (for instance, how to add support for AlteraSoC?). This would both motivate people to add this support, and shred a bit of light on all the manipulations performed during the compilation process.
These documents are available (training material and platform guide) – not searched enough, sorry!
They are actually being updated and the process is being significantly simplified and improved. Stay tuned.