I would like to have differnet Skype-addresses but only have to be logged in to one account to accept calls. Much like it works with Trillians Meta-contacts but the other way around.

Say I sign up users "MeAtHome", MeAtWork" and "SecretMe" but I want to be available and accept calls to any of these. So I choose to direct any traffic to these accounts to "MeAtHome" for instance.

Easy to implement and great feature!

Also, I would like to have the possibility to charge one account for my SkypeOut traffic regardless of what account is used.

Wouldn't it be better to have groups of contacts for one account?
(eg Group1 = MeAtHome, group2 = MeAtWork, group3 = SecretMe)
For each of the groups you then could set your status (and if offline, no incoming calls accepted!!).
I think that would be easier to handle than different accounts! This especially is more flexible for such activites as SkypeOut billing account!
Moreover you will only have to login to 1 single account, not 3 different ones (where you would have to remember passwords and usernames).

Maybe for running multiple account in parallel, would be easy if you simply run multiple Skype session at the same time... but would not be as easy for SkypeOut or \"cross-answering\"!

See above