I've made some progress on this-at least for those who use it tethered.

On my 3g with 3.1.2, the following stops the drain and allows it charge(slowly).

1) Iphone Settings, Wifi, Off
2) In MiWi, set Wifi tethering to OFF(top) and "USB and bluetooth" tethering ON(bottom).

Hope this helps someone. I still have no idea why it's such a sporadic issue, but since it reared it's ugly head for me this morning, this is the only fix(workaround) that I've found.