If Mauku can't connect or has some oddity it will drain the battery. Rare but it happens.

I know you're using SKYPE but I have had Gizmo kill the battery in short order. Remember anything that polls the network will drain the battery some.

I don't know which IM program you're using but I've found that the built in has less of an impact on the battery than pidgin.

Lastly, I don't know if you are using the built in mail client but if so, if it screws up, your battery is toast.

I'm running an 800 with a 2+ year old battery and I can still go all day so long as I don't hit a flash website or have the mail app go nuts.