the butt is more out of shape than the legs.
Specifically, I was okay to ride longer than the 30 min I got in, except that I just couldn't sit in the saddle any longer.
By my heart rate monitor I did 30 min with an average heart rate of 143, resulting in ~ 411 kcal burned. None of that is very impressive, but the important thing for me is that I was able to finally get started. Hopefully next week's update will be a wee bit more impressive.