Pros: The manly way to haul your kid around, comfortable.
Cons: Can't see what the kid is up to, putting pack on is tricky.
When I found out that a one-night stand was coming back to haunt me, I knew that I'd need to get the mandatory baby stuff for when I get the little critter on the weekends. So I didn't want a stroller - too girlie for me. A backpack seemed like the natural solution. The little guy loves it - gets a good view of the world around him and he's happy and comfortable.
I recommend making sure the pack fits you properly before putting Junior in it. It's very adjustable and will fit a variety of body sizes. Just remember that the hip belt distributes plenty of weight to your hips... shoulder straps are there primarily for stability and balance. Everything should be on snugly, but not so tight that you'll cut off circulation to your limbs either. Pack should not bounce while walking. If you put most of the weight on your shoulders and you'll feel it within minutes!
The only thing that I don't like about it is that you really need someone there to hold the pack steady while I put it on to make sure I don't accidently knock it over. While the flip-out stand is quite stable and sturdy... remember that the unit becomes very top-heavy when Junior is in it and the stability factor decreases - especially if he's a squirmer. Other thing I didn't like was that when he fell asleep, he was using my head as a pillow - not the most comfortable thing for my neck - so try not to take the kid out in it when it's near his nap time. You need a good park bench or picnic table to help set it up here - getting it on your back and standing up from the ground would make most chiropractors wince. Also, it would be nice if it came with a rear-view mirror so I can see what he's up to (but I think you can order one on the net somewhere).
Overall, this thing rules and I'm glad I bought it. The kid loves it - doesn't get bored and knows where daddy is all the time. It's definitely an attention getter - everyone always asks me where they can get one.