Investors have fled Carbonite like Carbonite fled Rush Limbaugh, but, as they say, correlation is not causation, so it’s impossible to know for sure whether Carbonite’s stock has plummeted because the back-up company withdrew its support for the top talker — or just because. Nevertheless, the facts are what they are:

Since the market opened on Monday through its close [yesterday], Carbonite stock (NASDAQ: CARB) has plummeted nearly 12 percent, outpacing the drop of the NASDAQ index in that same time period by nine-and-a-half points. It was also one of the biggest decliners on the NASDAQ on Tuesday.

It’s hard to think Carbonite CEO David Friend’s smug retraction of support for Limbaugh had nothing to do with his stock’s downward trend, though. Consider, for example, that conservative pundits have made a point to call Friend out by name for his decision to pull advertising and to continue to criticize Limbaugh even after he apologized. Why single Friend out from among the dozens of advertisers to reject Rush? For one thing, Friend continues to support with his advertising dollars Ed Schultz and Howard Stern — two men who’ve been known to use their fair share of foul and derogatory language. That makes Friend’s reason to leave Limbaugh — which was, I remind you, to “contribute to a more civilized public discourse” — a little suspect.

Conservatives have also noted Friend’s ties to Obama:

Carbonite CEO David Friend, currently under fire from conservatives for pulling advertising from Rush Limbaugh, is an Obama donor according to records obtained by the Federal Elections Commission.

According to the FEC, Friend donated $2,000 to the Obama Victory Fund (a joint fund-raising committee with the DNC) on July 1 of 2008, and $2,000 directly to the campaign on July 31 of 2008.

Is the plunge in Carbonite’s stock a warning to the other 29 advertisers (some estimate it’s actually 35) who’ve halted commercials on The Rush Limbaugh Show? Perhaps. As I’m sure Rush’s advertisers know from their days reaping the benefits of their patronage, Limbaugh has a loyal listening audience.

As far as this half of the controversy goes, I’m really not outraged. Rush had the right to say what he said — however tasteless and stupid it was to say it — and advertisers have the right to take their dollars elsewhere. Trouble for those advertisers is that consumers have that right, too.

Update: On his program today, Rush explained that he didn’t actually lose 28 or 32 or 35 or whatever number of national sponsors. The “lost sponsors” are actually local advertisers who simply requested that their commercials not run during Rush’s show.