Keep in mind that your income will quickly decline as all those asics come online. Bitcoins' appreciation might help lessen the impact somewhat. Play around with the difficulty and the rate based on what you think might happen. I think buying btc and waiting for asics is the better choice, but that's just my guess.
+1
Once those things hit, the day of the current gfx cards will be over. You will still use them for the other cryptocurrencies. In fact I am using mine on LTC. Trading them for BTC @ a higher return than if I had my machines mining BTC.
I reckon those ASIC machines will ship, but the question is when. I was about to order 2 of the 60Gh/s machines, but they went and doubled the price and reduced the Gh/s to 50!
I guess a current investor who wants to mine has to just think:
are those ASIC machines real?
When will they ship?
If I invest in a rig with normal gfx cards, how long will they be able to work for me, before ASICs make them null and void ?