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 online travel company Expedia (NASDAQ:EXPE) plunged on Friday after the company came up short of analyst estimates when it reported its fourth-quarter earnings. By noon, Expedia's stock price was down more than 11% from the previous day's close.

So what: While Expedia's revenue, which grew by 19% year-over-year, only missed analyst estimates slightly, non-GAAP adjusted EPS fell well short, coming in at $0.86, a full 15 cents below analyst expectations.

Operating profit contracted by 32% year-over-year, with adjusted net income falling by 10%. Profitability was up strongly for the full year, but this was overshadowed by the disappointing fourth-quarter results. A 28% rise in marketing expense during the fourth quarter helped drive down the bottom line, as did a $25 million restructuring charge.

Now what: Guidance for 2015 was cautious, with CFO Mark Okerstrom stating during the conference call:

We are expecting a deceleration in revenue growth in 2015 on headwinds from Travelocity implementation, further impact from the reduction of our hotel margins, the negative impact of foreign currency and the continued success of our loyalty programs.

Expedia does expect EBITDA to grow by 10%-15%, excluding the impact of its Chinese subsidiary eLong, during 2015. However, eLong itself is expected to report negative EBITDA. All in all, Expedia's guidance was far from encouraging, and it's not surprising that the stock was punished as a result.