Problem is, the C range tires DO NOT have the wieght carrying capacity. Take for example a stock size tire for our trucks, the 265/70-17 size. In a C load range the tire is rated for 2470 lbs per tire, the E that comes with the truck is rated for 3195 lbs per tire as is a 285/70-17 D rated tire. That would be a payload loss of 1450 lbs, pretty substantial. It would also put the front tires at risk because I think the front of a CTD is right around 4400 lbs, very close to the 4940 lb total capcity of a set of stock size C rated tires. A couple heavy set guys in the front seats could put you over! So, no, the letter still makes no difference to me but the load capacity just isn't there making C's a poor choice in my book.
You mention that the C rated tires are cheaper. Did I leave the impression somewhere that I buy these D rated tires because they are less expensive? That isn't the case. I have run several sets of BFG KO's and have a set of Wranglers for different reasons. I buy them for the severe snow rating they carry, the extra durability of a three ply sidewall and more aggressive AT tread, and I completely agree with your assesment that the bigger tires look much better on the truck. It just so happens that to get that combination of features in a comparable to stock load rating that I have ended up with D rated tires. To answer the question directly, NO, the letter means nothing to me. Like I have said a hundred (or more) times here, the wieght rating of the tire is the only number that matters.
I know that one time I shared my experience with two different brand, same size, same rating tires for my motorhome. I had Michelins on there, they had some dry rot and I had a trip planned. On short notice all I could get were Firestones, same size, same E rating. While changing the tires out I noticed a huge difference in the sidewall thickness. The Michelins where about twice as thick in the sidewall. I think the instability some may feel going D to E or vice versa has more to do with differences in tire brands and construction that the letter rating. These were some seriously flimsy E rated tires, even at full pressure I could feel the difference on the road. I'm not really trying to rip the Toyo's or Nitto's but maybe you NEED 80 psi to stiffen those up to the point where they are as stable as a better constructed BFG, GoodYear, or Michelin in a lesser letter catagory?
How about this concept. Load capacity is determined by the tires ability to dissapate heat. Too much heat and you have a tire failure right? Heat is generated by sidewall flex primarily, the more it squishes down as the tire goes around, the more heat generated. One way to lessen this flex is to increase tire pressure. So an E rated 265/70-17 tire is rated for 3195 lbs at 80 psi. The 285/70-17 tire is rated for 3195 lbs at 65 psi AND has a taller sidewall. It would seem to me that the E is actually the weaker of the two because it needs more pressure to carry the load right? Common sense tells me the 285 D tire must have stiffer sidewalls to carry the same load with less pressure right? Otherwise, if you guys are right about this, wouldn't the taller sidewall tire with less pressure in it have to be rated for a lighter load because of too much sidewall flex? Fact is, it is rated for exactly the same load. Do you really think the tire manufacturers would put that load number in lbs right on the sidewall if it wasn't true? Can you imagine the liability? There is no way you can convince me as a generality that D rated tires have weaker sidewalls than E rated tires. Look at the facts and mechanics of the whole thing, it just doesn't make sense. Your milage may vary but my experience also tells me there is no problem.
There is no reason to fear a quality D rated tire..... just put the kool-aid down and step away
Attention: TDR Forum Junkies 
I'm pretty darn sure I have pushed them.
I'm gonna hang around and wait for someone to tell me how having 10 plies is better than having 8 plies next. Of course, no modern tire for a light truck has anywhere near that many anymore but it sure is funny to read a post from someone who believes it. Or the more sidewall plies, or stiffer sidewalls, or... ... . :-{}
