A friend of mine has developed some underwear that really increase sitting comfort on long rides (at least they do for me). They're called SitRelief Shorts by Lipowear http://www.lipowear.com
These padded shorts have been developed for people who have a medical condition called lipoatrophy (i.e., a loss of body fat, typically in the butt and thighs). While I don't have this condition, I do not have much fat in those areas and even sitting on a Russel saddle on my GS my backside gets a bit sore after a few hours. So I thought I'd give them a try.
My first ride with them on was a 450 mile back roads ride from Albuqeuerque NM to Prescott AZ. The temps that day were moderate to warm (50 in the a.m, mid-80's in the afternoon). When the temp got up into the mid-80's the padded shorts started getting warmer than I'd like. So while my backside appreciated having them on, I did not wear them the next day when I rode from Prescott to San Diego across the desert via Yuma. (Now that day was hot till I got over the mountains.)
After a professional meeting in SD I rode up to see my friend in Orange CA. I was a bit concerned about washing them as they're not cheap shorts. He reassured me that tossing them in the washer and then dryer was OK though and that's how I cleaned them. Simple.
I next wore them on the ride from Orange through the LA basin and up to Pismo Beach (via San Marco pass, sweet). I was glad to have them on for this 240 mile jaunt up the coast. I washed them again when I got to Pismo and then subsequently used them on the ride up the rest of the coast to Seattle. Sweet.
The only downside to these shorts as I see them are 1) the cost [$69] and that I think they're too warm to wear when temps get up into the 90's. That said, my road bike riding shorts are $50 and aren't nearly as comfy as these for riding the GS.
As a disclaimer I have no financial interest in this company. I have known the developer, Terry, for a number of years though and consider him a good friend. I wouldn't be endorsing these shorts for riding though unless I thought that many of you with scrawny, er, lean, back sides might benefit from them. Edit 9/18. See post below about my having invested in the company yesterday.
The fabric is high-tech synthetic, the padding is perforated medical grade foam, and they're made in the U.S.