Just finished the Alcan5000 and used these shorts to help combat a chronic tailbone issue.
I ended up wearing them over bike shorts so that I could minimize the sweat factor and continue to wear the shorts day after day.
I rode the entire 4800 miles without any issue with my tailbone! Now, I did end up with a little monkey butt late in the event but I don't believe the SitRelief shorts were to blame.
I believe these shorts were one of the best "comfort" investments I made in preperation for this event.