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: Shares of electronics retailer Best Buy (NYSE:BBY) have dropped by as much as 17% on Thursday after the company released strong holiday sales data  that was immediately undercut by some rather dire sales projections for the first half of this year.

So what: Best Buy's domestic comparable-store sales grew by 2.6% after accounting for installment-billing benefits, and its enterprise segment's comparable sales grew by 1.8% after excluding this benefit. The company's online sales continue to be strong, as they were up 13.4% over the year-ago period, with "more than half of [Best Buy's] sales growth shopped from [its] stores," according to CEO Hubert Joly. Only Best Buy's international segment saw weakness, as comparable sales dropped 3.6% overseas.

However, Joly also warned of "external pressures" such as deflationary pricing, weak post-holiday demand for consumer electronics, lower interest in extended warranties. Combating these issues will "put year-over-year pressure on [Best Buy's] non-GAAP operating income rate" that could already be happening during the quarter now in progress. The bottom line is that Best Buy's enterprise comparable sales will be flat to down by low single digits, and non-GAAP operating margins will shrink by roughly 0.3% to 0.5% year-over-year.

Now what: It's hard to feel too bad for Best Buy shareholders, who still have a 40% gain over the past year even after today's plunge. Best Buy's stock remains quite cheap, and its dividend is relatively strong for a major specialty retailer. The warnings of weakness to come anticipate only a small slowdown, not a complete collapse, and Best Buy's problems seem to be tied more to a consumer hangover than to any company-specific problems. Given that this pullback is based upon short-term projected results and not long term business performance, today might serve as a good entry point for investors looking to take long term positions in the retailer.