Fitness Fun: Run or Walk?

I used to run with the best of them.  Ok, not the best, but I did the whole track and cross country thing in high school.  I still ran throughout college, but with less tenacity and in shorter bursts of dedication.  Signing up and training for the Marine Corps Marathon back in October was the biggest burst of running I've done in a while!  And, you know what?  I'm not sure I enjoy it much anymore.  When I run, I feel old and rickety and sore for DAYS.  And my knees and hips kill!  Oy.

However, I still love to exercise.  Yoga is my newfound love, and I do it regularly.  Also, all year I've really enjoyed walking!  I live right by this great path, and it's awesome to take a long walk and clear my head.  With winter settling in, I'm trying to find a good workout alternative for when I'm not in yoga.  Yesterday, I had a great workout!  Brought an unread magazine, and set the treadmill at 4mph at a 2.0 incline.  It was a great, brisk pace, and the bit of incline really got my glutes workin'! 

What's your workout routine?  Have you found that it's changed significantly over time?  Ever scale back your workout?  Did it make you feel old and weird, too?