Well, if I'm not mistaken, the three players in this equation are Empathy for chat, Gwibber for microblogging/broadcasting, and Ubuntu One for cloud storage. I'm sure that Empathy and Gwibber can be added to the startup items (under System >> Preferences >> Startup Items), and I know for sure that Ubuntu One is already in that list.
I know that's probably not as elegant a solution as what you were hoping for (a simple checkbox would be nice), and I also don't know whether launching these from the startup menu will open their respective windows or not, but at least it's a start. Let me know if it works for you!