With virtually unlimited posting space you can do long descriptive paragraphs without being cut off. You can add vast amounts of people to a group conversation for events where you might be playing more than one character, or for those that can't log into game for an event (we've gotten up to 12 people in a conversation/skype rp event before if I recall).
Our group usually posts pictures of whatever toon we happen to be rping at the time in the profile picture space provided to let people know what we're doing or what we're in the mood for. Plus it's an amazing way to quickly file share and toss around ideas without the limitation of posting space. For privacy if you're doing an rp that you don't generally want anyone to see just yet, or just to do an rp and then copy/paste it onto your guild's forums!
The more I kick this idea around in my head, the more I'm really seeing some potential. I know I for one would love a way to RP when I can't be logged in for whatever reason. In the past, I've usually just pinged people individually for RP, but it would be cool to have a platform we could use when characters are out in the open somewhere... simulating the in game environment, basically.
I'm curious about how you guys work out logistics (like how you set the scene for your Skype RP interactions and such). I should probably start a new thread on this. >.>