I have seen it done. In doses up to 40mg. Apparently it was nothing special, no rush or euphoric effects to speak of. Onset of effects however, was rapid. Though it must be said that the person who atempted this is very tolerant to stimulant drugs via the IV route, and is quite a hardcore drug user in general.
I don't think desoxy is worth injecting, but if you must try it, start with 5mg or less, to be on the safe side.
Edit: ah, just noticed this thread is over a year old..