How Long Should a Child Stay in a Stroller?

Boy on Bugaboo Standing BoardMany moms, especially those with an infant and a toddler often wonder at what age their kids should spend more time walking and less time confined to a stroller.  I've seen parents wheel their 4-5 year olds around city streets and at the time I was carefree and childless so I found myself appalled.  I thought by the age of 3 certainly, kids need to learn how to use their own two feet.  But convenience often outweighs lesson teaching, boundaries and effort when you are working or have more than one to think about.  My first stroller was a Bugaboo Chameleon so I was pretty pissed off when the Donkey was unleashed earlier this year.  Bugaboo Standing BoardI was not about to spend $1200 on a new stroller.  I did some research and settled on the City Select because I loved the multiple configurations and flexibility it offered.  And I vowed to list my Chameleon on Craig's List and get at least $400 for it.  But, even the City Select is a beast.  It's long, heavy and just doesn't handle in that great way the Bugaboo does.  So I have debated keeping the Bugaboo and adding a standing board.  But before I spend $99 I wonder if I am setting my expectations too high for my almost 2 year old.  She loves to walk but if pushed to the limit will likely want to be picked up.  Will a standing board be the answer?  Take a look at this boy in the picture, seems like he is uncomfortable on the board, maybe too tall for it?...I am going to do some more research on this one.  Let me know if you have any experience with the standing board.