(I've moved my blog to tolik.me and some posterous comments are now gone)
(The post is edited, as some of these games were "acquired" or "taken down" by variety of companies, so the phrasing is limited to providing samples of "clones", not "pirated games")
Our friends have recently launched a treasure hunting game. But during the time we develop an A-class product, 3 other companies would enjoy the leadership in pirating AAA-class products from mainstream social networks. Here are some of the examples.
Last year pirates were battling over Restaurant City in Vkontakte, launching... several applications with different pirated localizations and... successfully updating them every month by ripping off content from the original game! They ended up battling with each other, ending up with 90% discounts on pirated content... One of the "companies" even went as far as to become a platinum sponsor of a social conference and got thrown out of there (hah!).
As we've developed SuperCity (we were 10 people at that time and SuperCity was developed by 6 people), the first social sim/tycoon city building game (with over 6 million players in Russia), we didn't know what to expect. By the time we've organically reached 100k MAU on Facebook, we got poorly cloned for the first time. It was a re-skin of a farming game with poor vector buildings. We laughed. It backfired 3 months later, when the game started to outperform our title with "bigger" marketing efforts.
When bigger guys have released a deeper, more comprehensive title (Social City), we got inspired to work on Legacy of Rome and we hit it right - Playfish and Playdom followed our case with My Empire and City of Wonder - by the time we were live in Russia. BUT... It's hard to compete against pirates who spend pennies to rip off and clone the best content.
In 2010 there were at least 3 Social City rip-offs in Vkontakte. Initially they were 100% rip-offs reusing original UI and graphics. But as they got first profits, "companies" have ordered cheap-ass art to replace pirated content... And they've fired back at us, stealing DAU with "deeper, more comprehensive experience" that costs pennies to produce.
It happens with many games and genres, depending on how tough they are protected. Sometimes it happens on the level of tradedress violation, sometimes it's a 100% rip-off.
6 years ago when I've produced casual games and worked on dozens of Xbox Live Arcade games, we were sure there's no way to decompile someone else C++ game, change texts and graphics and "publish" it somewhere else. Yet there were blatant casual game clones with A-quality production values. Even though they were blatant, they had 100% of content produced from scratch (except the game design) and took at least half a year to produce (except few rare cases of "pirates being bought out by publishers"). Few companies have battled with each other, spending hundreds of thousands on litigation....
With Flash, you have to worry about protection even more. SuperCity and our other games have one of the toughest Flash game protection schemes with multiple content and code encryption passes, thus we were never directly pirated "as is". And years later, I'm not actually sure if this is actually a good thing.
Our graphic content was stolen just once with a simple "PrintScreen/crop" technique. I was at a local social network conference recently and was expecting for the company representatives to show up, but well, they didn't come and they still utilize our background assets on a live application...