Oculus does have a real, physical, available product - I've used one personally that my friend bought (albeit through the kickstarter page). There are definitely people who are interested and it actually worked relatively well. Maybe it won't catch on, but I don't think it's absurd like many other tech start ups.

Plus, they weren't bought for $2 billion. They were bought for $400 million in cash and the $1.6 billion in FB stock which is quite a different thing. If you believe that FB is overpriced, then they were really bought for a lot less than $2 billion.