UPDATE: Mint CEO Patzer responds.

Social media can be a glorious way to reach customers — and to let them return the love in a very public way. But, as Mint — a division of Intuit (INTU) — is learning, sometimes showing off how much people are talking about you can quickly turn into a business nightmare.

The story starts with a recent post on Mint.com’s “mintlife” blog. On Wednesday, the site posted an infographic by Ross Crooks that mapped out the effect of Arizona’s anti-immigration law on the rest of the country. The chart has since been pulled from the site (you can spy a cached look at the site here), but many people who saw it were quickly alarmed and took to the blogs.

The Atlantic’s business blogger, Megan McArdle, ran a piece today looking at some of the “facts” Mint was touting.

The most obvious whoppers are the claims that “about 43% of all Food Stamps issued in the United States are to illegal aliens,” and “about 41% of all unemployment checks issued in the United States are to illegal aliens.” Mint doesn’t give specific citations, but these claims appear to come from this article at “Charlotte Conservative News,” which itself does not cite any sources.

Soon others were following up and Mint quickly posted an apology:

[T]he recent blog post “The Economic Impact of Immigration” went too far, cited polarized sources and did not receive the editorial judgment and oversight it deserved. We regret it. It is completely unacceptable and won’t happen again.

Mint’s defense came too little and too late — according to none other than Mint.com. By the time the company had responded, the Twittersphere had lit up with outrage, all of which could be read on the front page of Mint’s blog. There, a blue box features a tiny bird opening its beak to the sky, the title TWEETS ABOUT US and link after link of Mint hate.

A couple of the ones up on the homepage include, “Why I deleted my mint.com account:” followed by a link to the WSJ on the topic, and “I just quit Mint.com over its lunatic anti-Mexican rhetoric.”

For those visiting the site to learn about the Best Cars for Carpooling, or to get Personal Finance Lessons from Dad, suddenly they were being exposed to a post that Mint very clearly wished they hadn’t read — even if the offending post had long ago disappeared.

Maybe companies shouldn’t take it for granted that any mention of them on Twitter is going to be good PR. On the other hand, some sound judgment on the front end could have prevented this particular media backlash.

Mint.com founder and CEO Aaron Patzer is slated to speak at Fortune’s 2010 Brainstorm Tech conference. We’ll follow up, and see what, if any, lessons can be gleaned.