Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: JA Solar Holdings (Nasdaq: JASO) lost 9% of its market cap Thursday. Bad news?

So what: Any other day of the year, a 9% plunge in stock price would be really bad news. Today, it's just par for the course.

Now what: But is it a buying opportunity? That's what everyone's wondering post-sell-off. Problem is, it's incredibly hard to say. On the one hand, JA certainly looks cheap enough. If you can believe the numbers, it's selling for just 2.4 times earnings -- literally giving you the chance to earn back your investment and play with the house's money in about two and a half years. On the other hand, though, JA burned more than $50 million in free cash flow last year, even as it claimed to be earning $267 million in profits. We haven't had an update on its cash-flow situation in more than six months.

So, do you want to buy JA Solar today? Depends. Do you feel lucky?

Well do you, Fool? Add JA Solar to your Fool Watchlist.