how much money can you make a day with a typical 60GH/s ASIC?
How long will it stay this good?
There are a number of sites that can calculate this for you. I use:
http://tpbitcalc.appspot.com/why does everyone rushes to buy ASIC?
Not everyone is rushing. In fact, the majority od bitcoiners are not buying ASICs.
When looking at the bigger picture, Niko is exactly right. The "rush" you're seeing isn't from the general public coming in to purchase equipment, it's from a few hundred of us dedicated miners here in this community.