How do you advertise a scent on television? And how do you make a product that was around in your grandfather’s era and has no connection to a celebrity or fashion label seem cool?

You do it with charm, wit, and low-key sales pitch that lets people discover and re-discover it for themselves. Old Spice, once associated with other antiquated brands 60’s medicine cabinet like Ipana, Brylcreem, and Hai Karate, has had a surprising resurgence, starting with a Super-Bowl ad, followed by viral, interactive videos.

Craig Reiss of Entrepreneur.com thinks this is an indicator of very big changes in advertising.

Last week we saw two days that shook the viral marketing world. Old Spice, a long-neglected — if not forgotten — Procter & Gamble brand unleashed a social media blitz that may have changed the rules of social network marketing.

The Super Bowl ad features former NFL player Isaiah Mustafa and it’s theme appears to be addressed to the women in the audience: your man might not look like him, but he can smell like him. Why to women? First, who do men want to smell good for? Second, who actually buys it?

The commercials were appealing, with a light touch.

What really took off happened five months later.

Wieden posted a simple message on Old Spice’s Facebook and Twitter page: “Today could be just like the other 364 days you log into Twitter, or maybe the Old Spice Man shows up @Old Spice.” And show up he did.

As people tweeted questions about manliness to the Old Spice Man, he began posting near-real-time video vignettes responding to the queries, all in character and with no small degree of humor as he stood bare-chested, abdominals front and center in a bathroom set with the creative crew and comedy copywriters of Wieden + Kennedy behind the camera furiously writing jokes and chasing down props.

In a two-day blitz, the team produced more than 180 video “shout-outs,” including a marriage proposal (she accepted) and exchanges with celebrities including Ellen DeGeneres, Demi Moore, Christina Applegate, Alysa Milano, George Stephanopoulos, Olympics speed skater Apolo Ohno, gossip blogger Perez Hilton, tech gadget blog Gizmodo, Stanley Cup champions Chicago Blackhawks and Starbucks (which now has 10 million fans on Facebook).

Instead of spending millions of dollars buying time on the broadcast networks, which recently posted another dispiriting set of eroding viewership numbers, the Old Spice team uploaded them — at no cost — to Twitter, Facebook, and YouTube. They quickly got almost 600,000 “likes” on Facebook and seven millions views on YouTube — not people who fast-forward thought an ad as they watch a show on their DVR but people who specifically chose to watch.

Reiss’ shrewd assessment of what works here is well worth reading. In particular, he notes the personalized, interactive, and viral nature of this campaign.

That is at the core of the Old Spice phenomenon. People started competing to be witty or provocative, making their best bets on what would intrigue the Old Spice Man to want to respond to them. Many thousands did not get a response, but it seemed like all of them did. And the ones that didn’t kept trying harder to impress the Man. Also, every blogger or celebrity who did get a response wrote about it. It was a badge of honor.

We can expect many more brands to pick up on this approach — and most of them will find out that it is not easy to be as engaging and innovative as Old Spice, two terms no one would have thought of applying to that brand a few weeks ago. For a trip down memory lane, see below.