One of my favorite and wisest writers, James Lileks
Has this to say about boom times:

Having lived through a few such panics – real estate in the late 80s, the Savings and Loan crisis, junk bonds, the dot-com nonsense – I can conclude only one thing: no one pays attention to their gut. Whenever real estate spikes, my gut always says it’s a temporary thing, because two-bedroom houses with a cement yard and a bathroom that consists of a bucket can't possibly be worth $800K just because it’s in California. Ditto the dot-com: start-ups like tentonsoftofu.com were getting millions of dollars with the usual vague projections: in the future everyone will be online, and since tofu will be more popular than ever, people will want to buy 20,000 pounds at a time if we offer the convenience of online ordering combined with free shipping. Most people thought it was nonsense, but the times were good, so enjoy.