Bump charged the night I got it and I was good to go since then. On 3G, my ThunderBolt drains slower than my Droid OC'd to 1.1GHz on CM7 but slightly faster than the Droid OC'd to 700MHz on PE4.2 did.
Procedure:
-Everytime you set it to charge, leave it alone until it gets a green light.
-Turn on T-Bolt then charge until you get a green light (> 6 hours).
-Unplug T-Bolt, turn it off, then charge until you get a green light (< 1 hour).
-Unplug T-Bolt, turn it on for two minutes (to drain some battery), turn it off, then charge until you get a green light (< 1 hour).
After this your battery will have been calibrated properly and you should easily last a whole day (8+ hours of light to moderate usage) on 3G. This is no different than other 3G devices. I also don't think you'll have to do this again for a long time (but it will be VERY handy when installing custom ROMs as any Droid veteran can tell you).
Of course, if you have chargers laying around, charge whenever you possibly can (this is a general rule for Li-Ion batteries anyway), but never ignore your battery (don't run off power instead of your fully charged battery as capacity gets lessened over time).