According to this article, Foursquare is well on its way to mainstream success.
Maybe if you live in a social media-friendly city like Austin Foursquare is well on its way to becoming mainstream; where I live--a suburb of Washington, DC--I can tell you that Foursquare has a LONG way to go before it becomes anything approximating mainstream. Using the same 5 points the Telegraph article used, here are my reasons why Foursquare is NOT poised for world domination anytime soon.
1) Discounts and Rewards-I've been doing Foursquare for many months now and this is how many free things or discounts I've gotten: one. I pretty much single-handedly populated Foursquare's database for the town I live in, plus some surrounding areas, have waited patiently (ok, sometimes not so patiently) through countless SLOW AT&T/iPhone checkins, and have hyped Foursquare a lot both in person, on my blog and on Twitter and this is what I have to show for it: I once got a free scoop of ice cream at Ben & Jerry's when I bought another scoop. That's it. I do Foursquare because a) I'm a nerd and b) I need to know about it for my job. If it weren't for the latter, I wouldn't bother--it's a lot of time to expect a person to invest for very little return.
2) Winning the game--I'm a 42 year-old woman who frequents supermarkets, 7-11 and drug stores; I don't give a shit about winning badges on Foursquare. I suspect that there are tons of other people who don't care about them either.
3) Honest reviews--See #2 above; I don't need to read reviews of the places I use Foursquare for. If I want "honest" reviews I use Yelp--and even I know that good reviews can be bought for a price--and bad ones removed for the same.
4) Efficiently managing the city--the city, maybe, but I don't see many businesses in the burbs looking to spend money on Foursquare anytime soon based on the low level of adoption that exists. I am the only one checking in the places I go and, while it would be nice to have businesses paying attention, I know they're not.
5) Increasingly insightful search--A search engine is only as useful as the data it's indexing. Foursquare can ink deals with whoever they want; the fact remains that if adoption and useage are low in most areas, there won't be much to index.