Go ahead mine with you 1500+ watt 3.5GH/s setup or whatever.
3.5 GH/s running off a USB port will crush your ROI Mr. GPU man. The only hope is ASICs flopping or not being super popular.
I have some disposable cash ATM and my Preorder number means at least 500 Jalapeno's have been ordered and everyone knows that we all didn't order just 1 Jalapeno.
Get ready for something like 1.7+TH/s coming online at least. Its going to hurt.
The window is closing fast, but you can still pay off a GPU rig before the reward half (assuming BFL can't deliver a product in October) depending on your electric costs. Come July/August, then your ROI is shot to hell.
Also, judging from the 900+ orders BFL already has, I'd say they ALREADY ARE plenty popular.
Lastly, the SC preorder thread already has a listed 8.8TH/s as ordered, and that's only a known 38 out of 900+ orders. I'd guess anywhere from 100-250TH/s have ALREADY been ordered from BFL.