I had the fun of buying Amex‘s $25 gift card for $15 the other day on Amex Sync, the new Amex Twitter Store. All I had to do was sync my Amex account to Amex’s Twitter Store page, joing the ranks of 621,000 + other people, and I was all set. The card was delivered via UPS three days later.

The program is similar to other “sync” programs that Amex has been running on Facebook (“Like, Link. Love,” FourSquare and Xbox. In fact, it replaces “Like, Link, Love.” And the offers will keep coming. Sixteen merchants have been initially signed up. Today’s offer on Twitter was a Kindle HD Fire deal for $149, or $50 less than you’d pay on Amazon. The offers are a mix of credit for purchases and at home deliveries. Another offer was $25 off $150 spent at Eastern Mountain Sports.

On Twitter, there was a little learning curve involved. While there is a very clear video on YouTube, now seen 1.2 Million times, there isn’t room for a lot of instructions on Twitter itself. When I didn’t get a confirm for a half an hour or so, I assumed it wasn’t going through., and tried to retweet it (like a lot of people).

But in the end, it was there; it was a fun, social experience shared with a lot of people; and it was definitely a new way of buying things. In fact, it was the most fun I’ve had on Twitter since WineTwits annual virtual tasting.

Is it a winning model for Amex? On its face, the economics of it are hard to figure (as it is with Small Business Saturday, which gives you $25 off any purchase made at an SMB).

Amex won’t say how many gift cards they made available, but they did sell out within a few hours. If they sold 200,000, that was $2 million (plus shipping). 500,000 would have cost it $5 Million. If we keep buying items through the Twitter store, though, that’s a low customer acquisition cost.

Amex also gets a viral effect going from everyone tweeting the deal. There is also a certain gamification element of waiting for the confirm and then doing it within the 15 minute time frame.

Is it a winning model for Twitter? Most probably. It is likely to be getting a commission on sales – its first non-advertising revenue.

Is it a winning model for merchants? Potentially, it could be huge.