From what I've read on flyer talk, domestic 1st class is just meh compared to international 1st class on some of the carriers where they have lay flat seats, private cubicles, 5* meals, pj's and slippers and even the in flight showers (Emirates I think?). I've had a few domestic 1st class upgrades (back when it was more about who you knew than your airline frequent flyer status) and some business class flights when someone else was paying and it is definitely a 1000% improvement over coach but... for me it's not worth the extra money.
@gryphonslair99 - it's too bad this wasn't a few years ago. The BoA companion pass used to be good for 1st class as well but now is only for coach.