I picked up a vented lens hood from 46MM VENTED LENS HOOD TILTED SIDES - eBay (item 150548241333 end time Feb-12-11 09:12:00 PST)
Just don't see why a hood is a good idea on this lens ...
Flare isn't the only possible undesired element. Any stray light hitting your lens reduces contrast. A hood helps somewhat with stray light as well.
If you want the best punch from any lens, always use a hood to reduce as much stray light as you possibly can... otherwise, if you're happy with what you get, ok too.
(I use the Leica-Summicron M46 metal vented hood, as well, myself.)