Here is a link to a rough draft of an Applescript which I have used to import my iGTD projects tasks and contexts into OmniFocus for testing purposes.

Only intended for testing and reference, and others are welcome to modify and improve it.

Note that it leaves all trees collapsed by default, so you may want to use View/Expand all in the left and right panels of OmniFocus after any import.

http://web.mac.com/robinfrancistrew/...OmniFocus.html