Financial and property bubbles are obvious on hindsight. When things are going up most people will think the rise is sustainable and many will even invent reasons to explain why it is sustainable. A few years, I went to Vegas for a short tour. I was completely overwhelmed by the extravagance of the place - the concentration of magnificient buildings, entertainment etc. From Vegas, I booked a day tour that took me Hoover Dam and the Grand Canyon. The tour guide told us how Vegas had become the fastest growing city in the US and the real estate in the area can only go up because the number of people in the city expanded every year due to the building of 'mega-casinos' which created jobs. Jobs bring people to the city...mega-casinos were highly profitable because the number of visitors to Vegas was expanding at rate that would filled the mega-casinos faster than they can build them. The guide was right because 3 years later the real estate in Vegas were up something like 80% - thanks to Greenspan's zero interest rate policies. At the height of the real estate boom in 2007, all the economic fundamentals looked like they can't go wrong. However, within 3 months, the boom turned to bust[Link].
I'm not too sure if counting the number of cranes seen from the Singapore Flyer is a good indication that we are in a bubble, but the video is a good reminder that we all the factors holding up prices such as liberal immigration policies, low interest rates and global economic growth can change abruptly.