Amazon.com (Nasdaq: AMZN) invested $175 million for an undisclosed stake in LivingSocial last month. Now we know what the social coupon site is doing with some of that money.

LivingSocial this morning announced the acquisition of Barcelona-based Let's Bonus, giving the company the overseas muscle it needs to try and keep up with larger rival Groupon's international expansion.

Let's Bonus offers Groupon-esque deals through 25 cities in Spain, Portugal, Italy, Mexico, and Argentina. Let's Bonus also offers travel-related deals, something that will also help LivingSocial keep up with travel deals publisher Travelzoo (Nasdaq: TZOO) as it broadens the global reach of its LivingSocial Escapes offerings.

LivingSocial is the distant silver medalist in this space. A report last month from Internet traffic watcher Hitwise indicated that Groupon is generating nearly 10 times the traffic of LivingSocial.

In short, if Groupon is worth billions, LivingSocial could be fairly valued in the hundreds of millions. In other words, Amazon's $175 million should have bought it a meatier stake in LivingSocial than we think.

Now that we're getting more metrics out of both Groupon and LivingSocial, we can begin to arrive at our own conclusions.

LivingSocial's press release this morning claims that it has "saved its more than 16 million subscribers more than $280 million" since its inception a couple of years ago. Groupon revealed in a press release earlier this week that it has more than 50 million registered users, saving them over $1.5 billion last year alone.

These are big numbers, but it should also smell like an opportunity for the companies diving into this model. Catching up to Groupon is unlikely, but sprinting past LivingSocial for second place is a realistic goal.

Travelzoo already reaches out to a base larger than LivingSocial with its weekly Top 20 email of travel deals, and momentum is building for the Groupon-like experiences it began discounting last year. OpenTable (Nasdaq: OPEN), Yelp, and The Knot (Nasdaq: KNOT) also threw their niche-specific hats into the ring last summer, serving up prepaid discounts for restaurant outings and wedding services. They know their markets. OpenTable already has thousands of restaurants on its reservations platform and completed an overseas acquisition. The Knot draws millions of unique visitors to its wedding planning website. Keep an eye on the next few quarters to see if these initiatives are paying off with incremental revenue backed by chunky margins.

It's been just three months since AOL (NYSE: AOL) began repositioning its Wow.com gaming hub domain as yet another daily deals website. It's already up and running in Philadelphia, Boston, and Washington, D.C.

LivingSocial has to know that it's vulnerable. It can be caught from behind. This opens the door to rivals that have been dying to dive in as well as niche-specific players. LivingSocial better make sure this isn't the last deal it strikes in 2011. It needs sprinting lessons.

Should Amazon have bought all of LivingSocial, or is a stake enough to kick the tires? Share your thoughts in the comment box below.

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Longtime Fool contributor Rick Munarriz wonders if social coupons will be a passing craze or if thriftiness is forever. He does not own shares in any of the stocks in this story. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.