Pretty sure originally, Skype didnt support video chat with the SGS.
They updated it to include a beta type version for the SGS.
Might be one of the problems......just get people to call you instead of you calling them.
Or call them and get them to call you right back if you want.
Or you can try Gtalk. It is pretty much the same, if the other person has a google account, and it works perfect!