I had the same problem as Nicolas, regarding my 3G iPod being almost completely discharged after just sitting for maybe 2 days. After hunting through several web pages, the unlikely suggestion of making sure ALL the iPod alarms were set to off greatly restored my battery life.
I can't remember what alarm it was, but it was nothing I was using (or hearing). Apparently, it defaults to on.
The only thing I can see that looks like this is the calendar alerm which defaults to "beep" and can be changed to "off".