well, everything is a compromise. when the wheel isn't forged yet still lightweight that means the wheel isn't going to be as durable.
i've never seen anything like that, and i'll bet this is an isolated incident. but i'm also willing to bet we're only seeing 15 x 6.5 and 16 x 7's from rota and not 15 x 7's and 16 x 8's because a wheel that would fit within their standards for weight wouldn't be strong enough.
personally, i spent the money and went with a forged wheel. this isnt' to say rota isn't good, because i think for the money they are the best deal on the market. especially the slipstream's and subzero's, which look excellent and only cost around 100 a wheel.
i would just worry about this type of failure while i was driving 70+ mph around a corner at the track.