MG:
Not strictly true - 500' from persons, vehicles, vessels or structures. During FI course last year, I spent a fair bit of time below 500' AGL in unoccupied pieces of countryside, at one point even doing a power recovery to a hover (apparently a bit late, according to Leon) in a field.
You can only "infringe" the 500' bubble when "landing or taking off in accordance with normal aviation practice", if memory serves.
And I'll second MD900's comments . . .