I have a Cuddlywrap, which is identical to the Moby wrap. Tying it really isn't that hard. I was shown once how to do it and was able to do it myself from then on. I have a Bjorn as well, both have their plus and minuses I guess.
Personally for the money you spend on a Bjorn, and for as long as you use them I don't find them overly practical. Claire is a big girl, at 7 months she's pretty much almost past the weight restriction for the Bjorn. Also, it's not comfortable compared to the Cuddlywrap.
With the Cuddly/Moby wrap you can use it up until they are toddlers... basically however long you feel like wearing your baby. If I had known how much I liked mine, I would've never registered for the Bjorn in the first place.