Depends on what school you are aiming for. I'm quite sure that the top 10 will ask for retake, unless the rest of your application makes up for it. The reason I say this is that one guy on this site got a 730, but a 78% in Math and the Wharton School asked him to take the test again.

They look at Q as more important (I think)

I'm the guy with the 730 and a 78% quant that had to take it again. The adcom at Wharton said that the 80/80 rule isn't hard and fast, but someone might look down on the 78% quant, so I should consider retaking it. Keep in mind I had this conversation in April, and the round 1 applications weren't due until October. I had lots of time to try to get my score up. My undergrad GPA is only a 3.0. I wanted to have only one weak spot, so I retook the gmat.

I would say if you're applying to a top 15 school, and you're not planning on doing a quantitative finance specialty, you're probably OK. If you want to do finance at Wharton, retake it.

I also found the real GMAT quant to be much harder than the GMATPrep quant. If I had it to do over again, I'd use that Manhattan800 or whatever (I forget what it's called. The one with the quant section geared towards those shooting for 700+.)

Good luck.