i only have one on the rear, it seems just about bearable, for the weight im not complaining, it gives great weight distribution for my bike to standard where front are light and rears are heavy.
by bearable i mean the grinds don't hold amazing, needs a thin as grinding disc (0.8mm? something like that) and i've heard people ripping nipples through the rim due to it not having any eyelets (but mines been fine since march, just try not to over tension it.)
lets face it, there's no perfect rim out there thats light and strong.
give it a go, you might not regret it.
steve