I just unloaded my 13 BFL on ebay and bought a chili rig. Just within the last couple of days, I've gone from .0019 to .0013 a block running at 35 gh/s. It's all about custom rigs that can turn out 100's of GH/s plus. No reason to buy the little stuff.

Also, remember this:
USB stands for yoU Suck Balls. Don't buy a USB miners.