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 e-commerce and marketing solutions specialist Digital River (Nasdaq: DRIV) plummeted 26% on Wednesday after the company's quarterly results and guidance came in below Wall Street expectations.

So what: Digital River's second-quarter EPS managed to top estimates, but a slight miss on revenues -- $90.77 million versus the consensus of $93.4 million -- coupled with a downbeat full-year outlook reinforces concerns over the trend towards tablets and away from PCs. Given its ties with Microsoft (Nasdaq: MSFT), however, many bulls believe that the company remains perfectly positioned for the Windows 8 upgrade cycle starting in the fourth quarter.

Now what: For the full year, management now sees adjusted EPS of $0.96-$1.08 on revenue of $378 million-$380 million, well below Wall Street's view of $1.22 and $405.9 million, respectively. "This recent softness has caused us to temper our expectations for the remainder of the year," cautioned CEO Joel Ronning in a statement, "taking into consideration weaker PC sales and uncertainty in the macro economy." While Digital River's strong relationship with Microsoft might make today's plunge an enticing short-term opportunity, the ever-increasing popularity of mobile devices make the stock a worrisome long-term holding.

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