I'm happy to get at least 3 stars on a skin, anything more than that and I'm excited.
The ratings however don't really affect the popularity of your skin, I'm sure there are lots of 2 or 3 star skins that get more attention (downloads) than 5 stars, it's all subjective. I pay more attention to the comments that are provided on my skins, the positive feedback I've rec'd has always been a great boost to me - I look forward to that more than the star rating.