I have the snugli. We used it briefly (btw 3 wks - 10 wks of age), you can't really put it on wrong. But you need to adjust it to fit your body frame.
I will say that the Snugli is not very comfortable, especially for extended wearing, and especially as your baby gets heavier. It does not provide very good back support. All the weight is on your shoulders, and your back will start to hurt.
We ended up investing in a babyhwak (www.babyhawk.com). It's super simple, super light weight, no buckles. It's a little more pricey than your average carier, but TOTALLY worth the money. I've been carrying my daughter in it, since she was about 2-3 months old (ever since we stopped using the Snugli). She is almost 1 yr now, and we dont' go anywhere without our baby hawk. She sleeps in it and all. We go on extended hikes, and I have traveled with it overseas and across the country. 4 of my friends have now bought it, and they are very happy with it as well.
so check it out before you torture yourself with the snugli.
Also, if you live in/near NYC. There is a shop that sells them, so you can actually try it before you buy it.
Good luck!