Look what I came across surfing on Instructables. http://www.metacafe.com/watch/714116...re_cable_mess/
It's about a charging box, it sure looks tempting to make something similar (I see it's dead easy) but I was wondering... Does that thing look safe to you?
Any possible fire hazard from so many wires in a such a small space? (I suppose it's grounded)
Doesn't look like a safety issue at all. You're not altering the wiring, and the plastic box isn't any more combustible than the housings of the electrical devices themselves.
I don't think heat buildup would be an issue for such small devices.
Transformers give off heat. If it didn't start on fire it might ruin the chargers by overheating them. Many manufacturers tell you not to cover them or restrict air flow to them. I personally wouldn't do it.