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 Pharmasset (Nasdaq: VRUS) soared a staggering 85% on Monday after Gilead Sciences (Nasdaq: GILD) struck a deal to buy the biotech for about $11 billion.

So what: The deal values Pharmasset at $137 per share and represents a whopping 89% premium to its Friday closing price. Gilead is making a huge bet on the booming market for new hepatitis C treatments, but judging from its 12% decline today, investors aren't exactly thrilled with the price being paid.

Now what: Gilead expects the deal to hurt earnings through 2014 but to add significantly to the bottom line after that. So while the short term looks bumpy, gaining a quick edge on giants like Abbott Labs (NYSE: ABT), Johnson & Johnson (NYSE: JNJ), and Merck (NYSE: MRK) -- all fiercely developing hepatitis C treatments of their own -- seems like a smart long-term move. In a market that is expected to explode to $16 billion in just three years, paying up will likely have some huge perks.

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