BBs all have Lithium batteries and they do not have "memories" as did the ni-cads. Keeping it on the charger and topped up is a good idea. Running it all the way down is bad.
Keep in mind that the 9330 is much more advanced device than the old 8300 series. There are more things that use battery power, more web apps that could be running in the background. Also, some OS' are not perfectly optimized for battery usage.
And this from our FAQ: Maximum Battery Life - BlackBerryFAQ