I've taken the Mundo out a couple of times now to run errands, in spite of her still missing some parts (RideThis, I'm looking at you).
As previously mentioned, I've pretty much ridden two adult bikes ever, one a short-lived vintage Schwinn cruiser and one my now-modified Bianchi Volpe. So I don't have a great depth of experience to draw on as I talk about riding the Mundo.
Riding the Mundo, I feel BIG. Being six months pregnant, of course, helps with this sensation. The Mundo, like my bulging belly, takes up SPACE. I'm aware of the width of the H-racks even during unloaded riding, and when on a busy bike lane-- say, eastbound on Hawthorne around 5:30 pm-- I was at first self-conscious about how much space I was taking, and how slowly I was moving in comparison to the zippy hipster fixies passing me. But with a bit of practice at it, the experience became more relaxed, and I became more comfortable with the pace the bike requires of me.
The frame is significantly stiffer than my Volpe, with the unyielding fat frame tubing sending more jolts and bumps my way than I'm accustomed to. It's not an unpleasant ride, but I was surprised at how much difference riding a less-compliant frame could make. However, this bumpiness is much less pronounced when the bike is loaded-- I think this bike is happiest when it is weighed down at the rear, which is as it should be.
The ride while the bike is loaded (I'd guess 70 or 80 lbs of groceries) is smooth and stable. I'm still getting the hang of starting and stopping while loaded, and have occasionally teetered before catching my balance after a sudden stop, but I think that is a matter of skill and familiarity, rather than a problem with the bike. Riding under load feels pretty much like riding any other bike-- except slower, and heavier. But very, very stable.
The biggest failure so far is the kickstand, a Hebie BiPod. Rock the Bike recommends this for "everyday loading" but not for "true cargo" loading, but I don't see the distinction: the BiPod can't hold the bike upright when I'm loading several sacks of groceries, and so isn't nearly up for my "everyday" needs-- I certainly wouldn't use it while loading a kid onboard. We'll be upgrading this part soon.
We picked up a Go Getter bag from JoeBike here in town and I think it is awesome for quick-and-easy loading of things like sacks of groceries (holds two full paper-size sacks comfortably) or for just tossing a thing or two onto the bike without worrying about proper loading technique. The only thing that I don't love about the Go Getter is that is it quite so portable: great when I need to get the groceries up the elevator, of course, but a pain to always have to take the bag with me when I lock up the bike. Mike Cobb, the Go Getter's designer, mentioned working on a secure, rigid, lock-able, waterproof "trunk" to fit onto the Mundo's rear rack. This sort of car-like security would be a real boon when carrying out car-like tasks, including multi-stop errand runs.
By far the biggest hassle of the Mundo comes from our current living situation. We're in a small downtown apartment, and the Mundo is too unwieldy for the stairwell and just barely fits in the elevator. Our neglectful landlords have allowed all of what passes for bike parking in the parking garage get filled up with decrepit, abandoned bikes, so without anywhere secure to leave the beast at ground level, we keep it along with the rest of the stable in our apartment. This means that when leaving the apartment, we need to get around several tight corners, put the front half of the bike into the elevator, tip it up onto its front wheel to tuck the H-racks in, and then repeat this maneuver (crashing into walls all the while) to get out again. This works ok if we're working together, but for taking trips solo (as I have been these past couple weeks) it's a substantial hassle. If the bike is loaded, it becomes even more precarious, and I usually end up tucking the prospective load into the elevator first, then squeezing myself and the bike in after it, and re-loading once I reach the lobby.
Fortunately, this hassle will only persist another month, as we are leaving our current apartment for a cute little Ladd's Addition bungalow (with bike garage!) at the end of August. In the meantime, though, the 15 feet between the bike and the ground certainly make me carefully consider whether any given trip really needs cargo capacity.