I'm sure it varies by project, but as has been said before when Google kills things, a lot of their projects require the core Google infrastructure (BigTable?) that isn't open sourced so it isn't possible to spin the project out.
I wonder if I'm the only one who thinks that Google could make a lot more money, and have a lot more impact, if they opened up the "core Google infrastructure" for [paid] uses by outsiders than Google AppEngine is ever going to get them.
App engine at this point is pretty much all their infrastucture opened up - you got short/long running processes, big table, blobstore, and map reduce. You don't get c or assembly but you get golang which is pretty close.
