cIf you have a website or even run an Internet startup, you should pay a lot of attention to your new visitors vs. returning visitors ratio. After all, you want to make sure that you're able to retain your customers. If you're fortunate enough to have a Google Analytics account, you won't overlook this parameter as it is shown on the first page of this absolutely awesome (and free) traffic analyzer. But what percentage of returning visits should you strive for? If you have no answer to that question, you may not able to draw any conclusions from the numbers.
Is 100% a good value? Of course not. It means you're not acquiring any new visitors. 0%? Not good either, since you're not able to retain your visitors in that case. So the answer must be somewhere between >0% and <100%. If this sounds like a non-statement to you, are you sure that you wouldn't have instinctively answered "as high as possible", asked about the optimal percentage of return visits? :)
To be honest, I don't know the correct answer to that question either (but I will look into it, and if you run a website maybe you should too!). In fact, there's not one single correct answer, as it depends on several factors such as "how often does a good customer of your site visit the site per week?". And these factors differ for different businesses.
Maybe the question is rather academic (but I still find it interesting). Common sense tells you that you must look at several parameters to draw good conclusions. If you look at your overall traffic stats, you should be able to tell if a rising return visit ratio is a sign of increasing customer retention or just a sign of sluggish new user acquisition.