Merrill Lynch and Stifel Nicolaus are passing ships -- or passing waiters, if you will -- on OpenTable (Nasdaq: OPEN).

It's been a pretty eventful for the web-based reservations specialist. Shares hit an all-time high on Monday, were downgraded by Stifel Nicolaus analyst George Askew on Tuesday, only to be upgraded by Merrill Lynch's Justin Post on Wednesday.

What's the menu special for today, OpenTable?

Post's upgrade -- going from "neutral" to "buy" as he bumps his target price from $50 to $63 -- leans largely on the recent test of its Spotlight initiative. Over the past few weeks, OpenTable has been offering discounted dining deals along the lines of Groupon and LivingSocial.

Limited-time offers have proven potent in cyberspace. Ask (Nasdaq: AMZN) why it acquired Woot earlier this year. For OpenTable, it could also represent some serious incremental opportunities.

Unlike the fixed -- and low -- bounties per seated patron, restaurants are willing to pay dearly to be featured as Groupon's city-specific deal of the day. A springtime round of financing valued Groupon at a whopping $1.2 billion -- in the ballpark of OpenTable's entire market cap.

Success in this niche is easier said than done, of course. OpenTable has a leg up through working relationships with 12,250 North American restaurants and another 1,878 overseas, but dining loyalty specialist Rewards Network (Nasdaq: DINE) is all about eatery deals, and it commands just a tenth the market cap of OpenTable or Groupon.

After all, since Groupon has a target on its back, it's really just a matter of time before Facebook, Google (Nasdaq: GOOG), or even Garmin (Nasdaq: GRMN) -- yes, Garmin-- make a play for aggressive location-based couponing.

For now, Post believes that Spotlight can add as much as $0.20 a share to OpenTable's bottom line by 2012 if the program is expanded to 20 cities by then.

In reality, it will probably be either far more -- because OpenTable has access to interested foodies -- or far less, if the test stalls. Yes, it can be a flop. If consumers begin associating OpenTable with half-priced eats instead of online reservations to the hottest eateries, Spotlight's success can come at the brand's expense and its relationship with miffed restaurants that find their potential diners redirected to marked down plates of foie gras elsewhere.

Opportunity's knocking for OpenTable. It better make sure that it knows the right way to open the door.

Have you ever used OpenTable for a restaurant reservation? Share your thoughts in the comment box below.

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