Depending on which firmware you are using (it is highly recommended that you use the latest firmware 20.2010-36.2 iirc) and how heavily you use the device, your mileage with battery life varies.

There are many factors that can effect battery usage such as (and this is not a fully exhausive list of the potential factors):
- Enabling R&D mode.
- Using any programs from extras-testing, extras-devel or any other experimental repositories/applications as per indicated by their respective developers.
- Having backlight at full strength when you do not really even need such bright screen. Even having backlight timeout set for too long can have impact on battery life when it is not necessarily needed.
- Having too many programs running in background. Having too many widgets running on the home screen and you having switch back and forth between multi tasking or switching to other home screens, etc.
- Having too many chips enabled (such as wireless chipset, bluetooth chipset, accelerometer chipset, etc) when it is not needed.
- Running programs that have significant impact on the performance of the device (firefox fennec/Nightly is a perfect example of this, so is OpenOffice). HAM (Hildon Application Manager) with many repositories enabled including extras-testing and/or extras-devel significantly reduces the usability of the battery, especially extras-devel).
- Not using autodisconnect program and/or having autodisconnect settings set too high for it to have any impact on saving excessive battery consumption. Note that this pont reinforces the point above on having too many chipsets enabled and when not in use. Also for me I find having 3G constantly enabled decreases usable battery life.

Points highlighted above answers to questions 1 and 2. Question 3, with listening to online radio stations could be issues with having bluetooth enabled and using wireless LAN to stream the music from online radio station. Both wireless LAN and bluetooth uses very similar radio band (2.4GHz band) and could easily interfere each other when both of those have antennas are in relative proximity of each other. Remember, N900 is a small device with at 4 chipsets using radio networks (wireless LAN, bluetooth which also has FM receiver capability, mobile/cellular connectivity, and FM transmitter). All these chipsets have antennas in close proximity as they share the same PCB board.