Do you have your ECID SHSH on file with Saurik? If not, downgrade's probably not going to be an option. Besides, what's wrong with Wi-Fi? It's faster than USB, and battery life issues can be prevented by just plugging in your iPhone.
I had hoped that a jailbreak exploit makes it possible to downgrade without this ECID of 3.0.
WiFi is of course not faster than USB, and having WiFi active on iPhone AND on the laptop will drain the batteries faster. Not to forget it is a seperate application and not as seamless as Apples 3.0 solution.
I feel pretty stupid for upgrading to 3.1 in the first place.. damn...