You can also see if your databases are huge. Receiving HTML emails loads pics and stuff like that.
options --> Status --> BB button and click databases and see where you have a lot of megs being eaten up. My browser cache always has like 1 meg, and I need to clean it frequently. Also, I have 2000 + emails a week, so that fills up fast, too.
Themes take up a lot of space.
If you upgrade your OS remove any options you don't use, but using BES I'm not sure which ones to tell you. 3rd party apps suck, like Viigo which loads all its articles into your phone mem and not your mem card (which makes me mad!).
Hope this helps.
BB8100>8800>8300>8310>8100>HTC Touch Dual>iPhone8GB>8300 again>Smsung Omnia>iPhone 3g16GB>Storm>BOLD!