I read in and old magazine that the 500+ was never actually released to the North American market. I guess that's not quite the case reading the other posts in this thread ;-)
I think very late A500s over here were actually re-badged A500+s. Or something pretty damn close. My 500 has a full label like a 500+ (though it only says A-500) and the same LEDs as a 500+.
I've never actually opened it up though (still has the warranty seal!) so I don't know what exactly is under the hood. Still only have 1MB of Chip RAM with the trapdoor expansion installed...