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 mobile ad platform specialist Millennial Media (NYSE:MM) jumped more than 11% early Wednesday after the company announced it has hired former Google executive Marc Theermann as its new executive VP of business strategy.

So what: Theermann previously served as Big G's head of mobile platform sales, where he managed publisher sales organizations for its mobile ad products. He was also responsible for the commercialization of Google's DFP Mobile, the DoubleClick Advertising Exchange, and Admob.

According to today's press release, Theermann will now report directly to Millennial Media CEO Michael Barrett and will oversee its "strategy, direction and go-to-market execution for business, corporate and international development and [...] accelerate the company's position with programmatic and native advertising."

Now what: Millennial Media stock still hasn't fully recovered from a massive 37% single-day plunge last month, which was collectively caused by its mixed first-quarter results, disappointing guidance, and the departure of its CFO. Still, Barrett insisted at the time Millennial Media has "an aggressive strategy" to capitalize on its market opportunity, and investors are encouraged that Theermann could help those efforts bear fruit.

But however impressive his credentials, Theerman is still only one man. And Millennial Media has made a habit lately of badly underperforming. As a long-term-oriented investor, that's why I'm perfectly content watching Millennial Media from the sidelines for now.

Steve Symington has no position in any stocks mentioned. The Motley Fool recommends Google (A shares) and Google (C shares). The Motley Fool owns shares of Google (A shares) and Google (C shares). Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.