Mine is horizantal. Stays cooler that way I've heard, plus i have no reason to put it vertically.

all my consoles i hang them from the ceiling by tight ropes tightly holding my ps3 and my ps2..so they can swing and not overheating..its a great method guys u should all try it!

I lay mine down flat. Mainly because I'm afraid its gonna fall off the shelf and smash onto the floor. though I don't think I'd have much to worry about then, I'd rather play it safe.

I lay my playstation 3 down for safety reasons mostly because I am in college and I don't want a drunk knocking over the system. Another pure aesthetic reason is that all the consoles I have had before my Playstation 2 and 3 had the opening at the top so you could not put them on their sides. so I couldn't get used to a system standing up and prefer it horizontal.

yes, ive heard one ps3 died from overheating cause some kid duct taped all the vents to keep the dust from getting in....

personally i lay mine on its side, cause the hdmi cable and the power cord looks ugly if i lay it horizontally.

Standing, more space efficient, and probably better for cooling, you know, hot air rises right?

 Shamelesssly stolen from Bod. :|

 OT: I lay mine down.

I stand mine up...and it feels cooler that way too (even though it's most likely not).  Sexy beast, eh?