I never wore a whole lot of makeup anyway, but I'd become convinced that 'good Christian women' didn't wear makeup of flashy clothes, etc. Makeup is really sort of a non-issue in the Bible. There's something like three passages that mention it at all, and in the context it's not saying yea or nay, but just mentioning it as in: she put on some eyeliner. Only Biblically.
If it's important for you to know what passages speak of makeup, they're: 2 Kings 9:30, Jeremiah 4:30, and Ezekiel 23:40. Those didn't really enter into any argument that I saw, however. The verse that I saw used, was 1 Timothy 2:9-10: Likewise, I want women to adorn themselves with proper clothing, modestly and discreetly, not with braided hair and gold or pearls or costly garments, but rather by means of good works, as is proper for women making a claim to godliness.
You'll notice that there's no mention of makeup in that passage. So why is it used? It's more of an extrapolation, an extension of the idea contained within the text. The passage, as I understand it, is basically saying, don't bling yourself out.
However, some people take it farther (and I was one of them) and wear very plain, dark clothes. No jewelry, no makeup, don't do anything fancy with their hair, etc.
I think, now, though, that it's not really about whether or not you wear jewelry. Aesthetically, there's such a thing as too much jewelry, too much makeup and then it becomes tacky and *waggles hand* ugly. But really, I think the passage is more about the importance of such things. As a Christian woman, it's not the shiny things that you wear that make you precious or good in God's eyes. It's the good works that you do, the hungry that you feed, the poor that you clothe. That's the 'jewels' you wear for God. The other stuff, wear as suits your tastes, and what is tasteful. I don't think God cares either way. Though He may cringe at some of the things we wear just because they're in such poor taste. :)
So that's my new rule of thumb. It's allowable, as long as it's tasteful, not tacky.
Which is a long way of saying, I'm wearing makeup and jewelry again.