same here, if i take too long to swap batteries then time is reset, i usualy swap them in few seconds and all is fine.

that is really odd. I swap batteries daily and have never lost my time settings. could it depend on the battery too?

Not the battery, situation start when the charge inside the phone runs out. If people who never experienced it why don't you guys try take the battery out now and press the power button and let it off without battery for 40seconds, then put it back in and start your phone. Now feel it? I guess you will

well I was thinking most batteries stop themselves from being fully drained by switching off the device but still power a system clock for alarms too. I was thinking maybe some batteries do this later giving less time where they power the system clock so there is actually less time to swap batteries once it had switched off.
Do phones have a small CMOS battery or capacitor?

It also happened when I just bought N900, but I figured later the shutdown button doesn't really shutdown the device immediately, thus removing the battery during shutdown in progress would cause some problems, like disappearance of newly created widget.

Either you need to wait or enter the following under xterminal (or create a command line widget) to issue the shutdown with sync:

Edit: Of course I didn't rule out the possibility of defects. Just try shutdown the device properly and see if it happen again.

Turned off my device, took out the battery for five minutes, put it back in, turned on my device, device is still merrily displaying the correct time.

Turned off my device, took out the battery, removed the SIM card, put everything back where it belonged, turned on my device, device is still merrily displaying the correct time.

Turned off my device, took out the battery, repeatedly pressed and held the power button for a minute or two (God knows why anybody would ever try to power on their device while the battery is removed...), waited for a minute, put the battery back in, turned on my device, device is still merrily displaying the correct time.

So, no: No matter what I do, I do NOT "feel it"...

A 2 min time out w/o the battery did not affect my device.