Boy, sounds like the guy is a real jerk and I see no liablility on your part whatsoever... of course here in GA you would have never gotten a certificate of occupancy without landscaping. But as I see it the builder built the house per the local codes, the inspection authority obviously passed it and the only problem you *might* have is with your homeowners association. You've abosolutely bent over backwards for this guy so any problem he's got should be with the builder or the homeowner's association or the local inspection authority; not you. That's what's supposed to be nice about a homeowner's association; it prevents neighbors from going after each other like that. I would at least ask the judge to have your neighbor pay for your time and any court costs that you may have.
I'd bring everything that Dan said and any other documentation you can get from the builder and local inspection authority and maybe even a copy of the covenants where it states that you have a year to put in your landscaping.
On the flip side... I'm not sure what the laws are where you're at but lots here are definately required to maintain their silt within the property lines with a silt fence that is capable of doing the job (usually a silt fence reinforced with chicken wire). If that landowner doesn't maintain the silt on the property then the inspection authority should be called and handle it from there on out. So, if your neighbor has legitimate complaints with the local authority having jurisdiction and you were told by the local authority to do something in particular and you failed to do so and were cited for it then the other homeowner could bring that information to court and you could have problems at that point. If he hasn't done that then I wouldn't think that he would have a legal leg to stand on.
Just my 2cents.