Nice grill Joe... I'm jealous.
OK, so we finally did the taste test on Saturday night.
Gas v. Charcoal... the TestSet upI went a little "nutty" with this experiment... maybe it's the engineer in me.

I got two prime porterhouses from the butcher Saturday morning. Threw them in the fridge until 30 minutes before grilling. Took them out and seasoned with kosher salt and freshly ground black pepper ONLY.
Preheated my propane Weber Gold Glass B (similar to the new Genesis S320).
Preheated my Weber One-Touch Gold with Cowboy Charcoal in a charcoal chimney.
After steaks were cooked, they were removed from heat, placed on a carving board, covered with foil and sat for 5 minutes.
Steaks were then cut and placed on separate, labeled plates.
After each taste, I rinsed out my mouth with Poland Spring water to taste with a fresh palate.
ObservationsThe charcoal actually preheated quicker. Maybe because it's got a smaller cooking area (volume), maybe because hardwood lump burns quick and hot.
The gas grill actually got hotter, as that steak was cooked about 1 minute sooner. (This could be controlled by adding more charcoal. I filled my 6-quart Weber chimney about 3/4 way full).
No flare-ups on the charcoal, one small (and quickly extinguished) flare-up on the gas.
ResultsThere is a noticeable taste difference between the two. The charcoal steak definitely had a slight smoky taste from the hardwood lump. The gas grill had almost two flavors. If you ate a piece that had a grill mark (the grates on the Weber are rather thick... about 1/2") you got a (for lack of a better descriptor) burnt flavor... but not burnt in a bad way... burnt as in a seared-smoky flavor. If you got a piece with out the grill marks, it tasted just of steak. I should note, for comparison, the grill grates on the charcoal and much thinner... maybe 1/8".
ConclusionsBoth steaks were delicious. And I wouldn't be upset if I was served either. I think it comes down to "what's your mood." If you want a little smokiness, use charcoal. If you want true flavor, use gas. Some things would be better on gas (delicate fish comes to mind) where you wouldn't want a smoke flavor. And conversely, some things would be better on the charcoal where you want that smoke-kissed flavor (burgers come to mind).