The main reason would be that anyone with friends/acquaintances on Skype but without their phone number can call them, and more importantly send messages.
I've got iskoot installed and the memory management is terrible. If logged in constantly, it'll suck up all the available memory in about 1 or 2 days. A Skype authored app would be great. Hope their beta turns into a general release beta.
yeah it'd use your minutes but thats the main instant messaging site i use so i would use it mainly for IM on my phone and save video calling/calling for my computer. i'd still be nice to IM my friends from my phone. my friend has it on his iPhone.