Pros: Easy on/off, comfortable for long outings or quick trips, weight range up to 40lbs.
Cons: May be too pricey for some, side-carry position not as easy or comfortable as front/back.
I honestly cannot say enough good things about this product.
Before my son was born, I had heard most baby carrier buzz around the Bjorn. But then I started shopping for cloth diapers, and I stumbled across a wide variety of slings and wraps. So for my newborn, I started with a ring sling instead. I loved the sling, but my husband wouldn't wear it. So when the baby was a little older, around 8 months, we went carrier shopping. This time I'd done my homework.
When I tried on the Ergo, my 17lb boy felt like he weighed nothing at all. I was able to get him into the front and back carry positions with relative ease, though the back carry was a little bit awkward at first. I balked at the price at first, but some of the Bjorn models are just as pricey if not more, and they won't last nearly as long. My son is now 25 months old and still loves being carried this way.
The shoulder straps are well padded and long enough for most average wearers. It holds the baby in a natural position that keeps the hips and spin in proper alignment for development, and it's obviously comfortable for them. The sleeping hood snaps to the shoulder straps for extra head support when the little one gets so cozy she just can't help dozing off.
Even though it's not designed for a facing-out carry like the Bjorn, the Ergo still allows the child to see enough of everything, including you, which encourages bonding and social development. The front carry is easiest, the back carry takes some practice, and the side carry requires adjusting the straps in a different configuration than front and back. The carrier comes with instructions and a DVD. It's more helpful to watch the video, though, especially for the back and side carry positions.
I never really got the hang of the side carry. I've seen a few parents use it that way, but I didn't find it to be as comfortable as the front and back carry. The only other drawback is that since the waist strap sits at or above the hip, sometimes I find wearing it, especially with my heavier toddler, causes my pants to slide down a little bit. Tightening the waist belt or wearing pants that fit properly usually solves that minor issue, though.
The carrier is machine washable, but the only parts that consistently get really gross are the straps where the baby will suck or chew, and most babies will chew on it, so I would definitely recommend getting the sucking pads to go with your carrier, too. They just velcro over the straps where the baby will suck, and then you can remove and wash those as much as needed so you won't have to launder the carrier itself overmuch.
There is also an infant insert to be used with very young babies. I never used one, since I got my carrier when my son was older, but I've heard that the "heart to heart" design is better than the original insert was.
See http://www.ergobaby.com for other colors and accessories for the Ergo.
See http://www.thebabywearer.com to look beyond the Bjorn for wearing your child.