If you install the new iOS4 revision 1 that has just come out, you might get the problem with your battery getting rinsed from a full charge to dead flat empty overnight again, the same as when the first version of iOS4 came out a few months ago. Once again, the update seems to result in "Location Services" ("settings" > "general" > "location services" > "ON" ) being set, which results in the wifi staying active continuously, instead of sleeping when not in use. If you don't make use of location services, just switch the feature off. This time, at least, your "Notifications" setting doesn't appear to get over-ridden by the update, as it did on the last update. Again, if you don't make use of this feature, keep it switched off, as this can also result in unexpected battery useage.
Arfa