I wouldn't care, but the polite thing to do is ask.
Related - I carry a very small cube splitter with me, (smaller than the link), which I've used countless times in airports, airplanes with seat power, hotel lobbies, and traveling. I've never been told no when asking to share an outlet with somebody, and if I'm using an outlet and see someone hunting around I offer the same. Best $5 travel accessory that exists IMO.
http://www.amazon.com/GE-Grounded-3-.../dp/B001UE7SC8