The most likely buyer will be Tripadvisor or Priceline. They both are flush with cash and Tripadvisor has been aggressively getting into the restaurant review space and has much broader penetration abroad in all the places Yelp isn't at. Tripadvisor also bought reservations tool LaFourchette and Yelp could be a way to get more into the US game.
Priceline owns OpenTable and Yelp could be an interesting way to build out more reviews and get more restaurants using OpenTable.
That makes quite a bit of sense also, tho restaurants only make a small fraction of Yelp's total reviews, yes they are the biggest single category but they are not anywhere close to being a majority.
I still think that it makes more sense for a C2C/B2C group to buy them which aren't focused on specific industries, and i do see Chinese and Indian tech/business giants aiming to own western companies a core strategy for their future.
I'm not sure if they are more than 50% but restaurant reviews are definitely way more than a "small fraction".
TBH at this point I'm not sure what can they sell, their user share might be a worthy investment however anyone which will be interested in acquiring Yelp e.g. Google, Facebook, Amazon etc. already probably owns most of Yelp's user base via other means anyhow.
Not to mention that people moved from Citysearch and their ilk quite easily on their own. People want Yellow Pages and will find a new site to satisfy that demand if the old one ain't doing it for them anymore. It's not like an upstart would have much trouble getting a list of businesses from tax or business registrations.
TBH at this point I'm not sure what can they sell, their user share might be a worthy investment however anyone which will be interested in acquiring Yelp e.g. Google, Facebook, Amazon etc. already probably owns most of Yelp's user base via other means anyhow.
And as far as Google goes Yelp (Ireland) has given them quite a bit of trouble in the EU in the anti-trust case against Google (heck they've spearheaded the "public" campaign against Google).
This pretty much leaves Amazon and Facebook to buy them, and I'm not sure any one of those will want to do it. I have a strong feeling that Yahoo will end up buying them which will result in another flop at the end. If not them then maybe one of the emerging Chinese companies like Baidu or the Alibaba Group (I'm actually thinking that it would make quite a bit of sense for Jack Ma to go after them especially they want to expand to the US and EU markets since they own tons of site that provide C2C and B2C services, heck this might be even more likely than a "US" tech company since Ali has a metric ton of money to spend these days)
That said I'm not sure if on the tech side Yelp is worth anything at this point, my personal view on that companies is that the main reason if not the only reason why they kinda dwindled and never really exploded is that they didn't find any clever use for their data which means they don't have some amazing IP to sweeten the deal for potential buyers.