Some tips for conserving your BlackBerry Pearl's battery are obvious-turn it off when you're not using it-but others are less so, like setting the camera flash to off or automatic. Here's a list from Research in Motion:
Exit camera viewfinder mode when not in use
Keep your camera flash set to automatic or off
Keep your backlight setting on low
Turn off Bluetooth when not in use
Use an authentic BlackBerry carrying accessory that automatically triggers the LCD to turn off.
As for that last tip, we're fairly certain any dark carrying case-or even an old sock-will do the trick. Also, pressing and holding the Mute button puts the phone in stand-by mode, which is another good way to reduce your power consumption, whether or not your phone's in the dark.