I think I may have figured out the problem:

I think I had my saddle too far back.

Originally my b-friend helped me position it. I have long legs (almost as long as his although he's a good deal taller) so he positioned it just like his. Seemed like a good idea.

But when I was at a bike shop last week I mentioned the discomfort I was having to the owner (I was a little embarrassed but I figured the guy probably knew his stuff). He immediately asked if I had tried moving the saddle forward a bit. He explained that although women often have longer legs than men because our arms and torsos are shorter we end up having to really stretch to reach the handlebars. The longer the stretch, the more pressure it places on sensitive areas. If we position our saddles back in the traditional (guy centric) manner, it makes the matter even worse.

I tried his advice. Moved the saddle forward just a bit and found that I was much less uncomfortable on my last two long rides. I felt pressure where I was supposed to: in my sit-bones not up front. Hurray!

I also tried tipping the nose down just a bit as you suggested Emily, and that seemed to help too. Thanks for the awesome suggestion!

Thanks to everyone for the help!! I'm hoping this keeps working. Hope everyone's out having a great ride on this gorgeous fall day.

-Sarah