No matter what you will buy, 3, 40 or 1000GH/s device.
The difficulty will grow with the total hash rate.
As you see, even with current difficulty you'll earn only several percent of the price of your ASIC in the month.
And every month the difficulty will grow.
Your used GPU is still valuable for gamers, your used (1 year) supa-dupa-rig will be useless for everyone.

I consider entering ASIC mining is much more risky than it was with GPU.

By the way, if someone believes in ASIC by october, then buying BFL singles right now is insanity, payback time is at least one year with current difficulty.

And I forgot about diminishing miners revenue

Of course, not!

Very good post. Does the author trust his wife or children?

If someone has several BTC or Mt.Gox USD and wants to buy online game electronically, e.g. from Blizzard store, I can help with that. Guys with good ATI card and without money on credit card, you're my possible clients. I'll take extra 10%. If you're interested, please p.m. for details. I do not plan to do it regularly, just want to study the demand. Let's see if I can prove that you can trust me  .

Still we have several months until that (and with 50BTC reward). So I'm buying 3 video cards right now, because I'll get my money back in 5-6 months. I do not have to pay for computers or electricity though .