I also love my Bob Revolution Duallie. My kids were 2.5 and newborn when we bought ours. They are now 4 and 2. For the first year of my daughters life we used the Duallie for our everyday stroller since my son still liked to be in a stroller. But now at the Big Boy age of 4, he likes to walk most of the time so we mostly use our single Bob Revolution (which we bought when he was 1 years old). If he gets tired, he just sits on the front foot part of the stroller. We still use our Duallie for family walks, jogs, and hikes.
I would go to a store like USA Baby where they have a large selection of double strollers and test drive them all before buying.
FYI:
My best friend has had 3 double strollers and the only one she likes is her Combi. She also has a Peg Perego Duette, which she hates and a Joovy Sit N Stand which is moderately likes. But she wishes she had my Bob Revolution Duallie. She LOVES it! But her DH said she can't get one until she sells the other 2 double strollers.
The Bob just glides over everything! We've taken ours camping, to the beach, and to the amusement parks. It's great! We load up our Bob with all of our beach stuff and DH pushes it over the sand with little effort.
LOVE IT!
If you do decide to get the Bob, wait for the sales at REI.COM. Normally the Duallie is about $525, plus another $40 for the infant carseat adapter, plus another $30 for the drink/keys handlebar console. I bought our single Revolution over Labor Day weekend (normally $350, I got ours for $299, including the handle bar console). I bought our Duallie over Memorial Day weekend for $425, plus $20 for the handlebar console. Just sign up at REI.com for email notifications. You can then order your Bob online, and then have it free shipped to your local REI store. They will also assemble it for you(there are only a few things that need to be put on the Bob) and demonstrate how it all works for free. So far this is place for the best deal on the Bobs.
If you are interested in a used Bob at a good price, try craigslist.com. I have seen several gently used and a few new in box Duallies on there, but they go FAST!