Investors dropped shares of Google like a hot potato Thursday morning. The stock, which closed at $458.19 Wednesday night, was hovering around $445, when last we checked, and it traded as low as $441 earlier. (By Thursday's close, the stock ended at $444, more than 3 percent down from Wednesday.)

So why are Google shareholders' panties in a bunch? A comScore report suggests paid clicks (which measures the number of times people click on ads that are sponsored by advertisers) dropped 3 percent sequentially in February.

Although paid clicks were up 3 percent, year-over-year, that still represents a dramatic falloff from the 30 percent to 40 percent growth rates of 2007, according to Bernstein Research analyst Jeffrey Lindsay.

"We think that these earlier growth rates reflect Google's large search share gains over Yahoo and Microsoft at that time and also paid search's gains over display advertising . . . Now we believe the primary driver of Google's paid click growth is the fundamental shift of offline advertising to online," Lindsay wrote in a client note.

The comScore report suggests that the downturn in paid clicks in January wasn't an anomaly, and that paid clicks could continue to deteriorate. Still, ThinkEquity's  William Morrison argues that it's something of a crock. He still expects a "solid quarter" despite weak paid click data.