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 GrubHub Inc (NYSE:GRUB) are trading roughly 6% higher this afternoon after leaping by as much as 11% in early trading. The food delivery network reported strong results for its fiscal fourth quarter this morning, and it appears set for more growth in the current quarter as well.

So what: GrubHub's fourth-quarter revenue rose 50% year over year to reach $73.3 million, with its GAAP earnings of $0.13 per share representing growth of more than 300% over the year-ago quarter's $0.03 result. Wall Street's analysts had only expected $70.3 million in revenue and $0.11 in EPS, so GrubHub's results were a pleasant surprise to the upside.

GrubHub is now offering first-quarter and full-year guidance for revenue and adjusted EBITDA in 2015. For the first quarter, GrubHub expects to earn between $24 million and $26 million in adjusted EBITDA on revenue in the range of $83 million-$85 million. Its full-year guidance now anticipates adjusted EBITDA in the range of $100 million-$108 million on revenue ranging from $335 million-$350 million.

Now what: Wall Street had only expected $325.9 million in revenue for GrubHub's 2015 fiscal year, so its top-line projections are clearly driving investor excitement Thursday. If the company's net income translates from its adjusted EBITDA at similar rates to those seen in the fourth quarter (from $10.8 million in GAAP earnings to $25 million in adjusted EBITDA), we might expect GrubHub to earn between $10.3 million and $11.2 million in GAAP net income, which ought to translate to approximately $0.12-$0.13 in GAAP EPS. This range is a little lower than the $0.13 in EPS currently projected by Wall Street's analysts, but those analysts were also expecting only $80.1 million in revenue for the first quarter.

With its current P/E of 213, GrubHub is a very expensive stock on a GAAP basis. However, it's benefited enormously from the dot-com 2.0 mania surrounding most mobile-focused companies, and it's undoubtedly growing quickly -- its full-year revenue projections anticipate growth of 32%-38% over 2014. This is a solid growth rate, but does it merit GrubHub's current triple-digit P/E? I would tread cautiously around this stock.