I absolutely LOVE my jogging stroller! With my first, we didn't opt to buy one. I used my regular stroller, but my husband and I started to go for 4-mile walks all the time. My stroller got thrashed and it was SO hard to push. We decided the second time around that we were going to do it right, and we ended up getting a very nice double-jogger with a detachable rain cover. We used it all the time, and still use it with my daughter occassionally. She still fits in it perfectly fine, we are just so busy that it is harder for us to manage walks now, especially with my oldest being 7 and needing to ride his bike now when we go for a walk vs. using the stroller. We have a great boardwalk along the water in the City that I live in which was our favorite place for walking, but I don't feel comfortable with my son on his bike down there, so we mostly use it in our neighborhood now (it has a convenient 1 mile loop, but it's just not as fun to walk around the neighborhood 4 times as it was to be down in the pretty scenic downtown area.
With a new baby coming though, I'm sure I will pull it out more and more. I think Connor was about 5 or even 6 when we stopped putting him in it, so I would say that we would have 80 lbs in the stroller and it was still very nice to push. Hills were a bit more of a challenge, but we could still easily do them.
We put Annelise in the stroller from the time she was newborn on up. The thing I really like about my brand is it has 2 different settings for straps and it also has zippers on the back of each seat so you can adjust for the baby to be fully reclined or sitting up. She was perfectly save. I would even strap her in with the Baby Bjorn on so I could front pack her if necessary. I think that most of the concern with regards to the babies being older is if you are on rough terrain and running more than walking. My stroller is a Kool Stride. It compacts down totally flat (you can even take the back tires off if you want and they are easy to get on and off). I got it at The Right Start (I'm 99% sure that that is the correct name of the store).
Hope that helps.