I've been thinking about open sourcing my source code as well. I've been trying to monetize a new mapping technique and I think there just isn't demand for it. So now I'm leaning toward open sourcing the mapping tech and trying to build a business the uses the maps to solve part of a larger problem (like real estate search, or business relocation).

My biggest fear would be one of the big mapping companies picking it up and taking credit for it. Though I'm sure this is unfounded and even if it happens at least people get to use it.