I have one suggestion to add to this thread...
...the best way to check cartridge bearings is to check them. Remove the cranks. No need to remove bottom brackets for this, but if you have the tools available you might as well. This is a good opportunity to clean the BB face and shell and check for any corrosion. To check the bearings simply spin them with your finger. You will very quickly notice if there is any play or roughness. If they feel buttery smooth, then you have nothing to worry about. If they spin freely, you need to think about replacing them, or stripping and re-greasing (if you are up to it and you have the necessary tools). It is normal for one side to give out before the other, so it will be obvious when this happens. Personally, given the low cost of new brackets, I think it better just to replace. In fact, you can do this as part of your scheduled maintenance depending on your mileage and the quality of parts used. I just did mine (FSA MegaExo) after 3,000 miles (DS was spinning freely, NDS was ok), so I know I am unlikely to get another 3,000 miles before they need doing again. As mentioned above, you can run cartridge bearings into the ground and you won't damage anything else. It's just about riding pleasure and efficiency.