You might want to post this question in the "Ask an MBA Admissions Consultant" together with a short bio. Depending on the rest of your application, they might say YES or they might say NO...

I'm in exactly the same same situation and I decided to retake. I did this for 5 reasons.

1) My previous prep was only a month and inadequate because I was under application deadline pressure. Also I focussed too much on difficult questions and not enough on mid-level problems which can sink your score because if you get mid level questions wrong you will never see a difficult problem.

2) I know I made a few blunders early on in the quant section that threw me off my game. Again, too much pressure on myself because of the deadline.

3) The areas I am weak in can be rectified with work (Number Properties, Inequalities and VICs, some Word Translations and Sentence Correction). I have already began to see huge improvement in my practice scores and confidence because I now know little rules about numbers and I now know strategies to approach specific types of questions that previously I didn't. And I can't over estimate the value of improving SC to my Verbal score. If I keep scoring like I currently am scoring in Verbal I will do very well.

4) 660 is just not good enough for most schools I am applying to. Remember 660 means your range is 630 to 690. I need to get the low end of my std deviation to 700... hence my target of 730.

5) My quant background is virtually non-existant -- high school calculus 15 years ago. I am a lawyer who assiduously avoided math after high school. So I have had to take two calculus classes (which has helped immeasurably with the GMAT prep) to build up my quant credentials. But even so, I need to get my quant score to a range where there will be NO concerns about my ability to handle b-school quant. And an 80%ile quant score will do that.

In short, DanaJ is exactly right. You need to consider your background, the schools you are aiming for, how much prep you did the last time, the reasons for scoring 660 and whether they can be fixed within the time frame you have, the likelihood of scoring worse etc. For me it was a no brainer. If you have time, take a week or two off (more if possible) and then restart your prep in a very dilligent and focussed manner.

If you've only taken the test twice, most schools will only look at the highest score, even if it was from the earlier attempt.

That said, the above advice is excellent. If your school's average is a 650, then your 660 should be fine. Once you hit a certain score (that varies by school, of course), the rest of your application becomes far more important.

Also, if you're only confident about moving up 20-30 points, I would argue that it's not worth it; there's really no difference between a 660 and a 680, and you're gambling that your score might actually drop. I've had students get into top-10 programs with 660s - granted, they had fantastic applications otherwise - but the GMAT is not the be all and end all of admissions.