Since I work as an electronics designer in a Research and Development
lab I do know what ozone smells like.  However as John pointed out it
is not any easy odor to describe.  Any time you get a lot of arcing and
sparking you get ozone.  It is a very distinctive yet subtle odor but
it doesn't really seem to have very many good parallels in everyday
life.

If you have ever serviced anything electromechanical in nature, like
a 1960 pinball machine, all the arcing and sparking of the relays and
stepper switches make ozone.  So, if you discount the smell of old
transformer and baked relay coils, when a pinball machine is operating
you can smell ozone on the inside.  I know that doesn't help much if
you have never opened an old pinball machine.

Laser printers make a little ozone.  You can kinda smell it when you
open the printer to clear a paper jam but the odor of melted toner and
the "heat" smell tend to mask it if you don't already know what ozone
smells like.

Arc welding makes ozone so you can kinda smell it there.  But again the
"metal" smell gets in there too so it is hard to detect if you don't
already know that to look for.

Sewing machines make an ozone smell because of the arcing of the
brushes in the little motor.  I think that it probably the best real
life example I can think of.

To describe the smell of ozone the best I can do is something like
this: You know how a camp fire smells when the rain puts it out - the
smell of fresh wet ashes.  New lessen that smell by about half, then
couple that with a an extremely slight odor of gasoline and you get
something close to the smell of ozone.

Hope that helps,

Ray Finch
Albuquerque, New Mexico, USA

PS: I got to thinking more about the smell of ozone and came up
with two things that produce that odor without other smells mixed
in: slot cars and model trains (especially the old Lionel trains).
The ozone smell comes from the arcing of the brushes or wheels on
the track as the cars or train go around the track.