Thanks for the replies, guys.
Until now I was a bit reluctant on using diodes because of the voltage drop (0.7V), and please correct me if my line of thought below is wrong:
Considering the minimum voltage required by the DS1337 is 2.5V, a 0.7V drop caused by the diode would bring a brand new CR2032 (3.2V) to the minimum required supplyby the IC. I am afraid that whenever the battery gets to 3.1 or 3.0V, it would no longer be able to power the DS1337 in offline mode.
@petethegeek
Thanks, I'll try that. I don't think I have any 1N4001 around, but I have a few dozen 1N4148
BTW: I am also planning on making a shield that will host a RTC + 4 X 24LC256 EEPROMs, all on a single I2C bus. I already ordered the EEPROMS from Sparkfun, but I just found out that Farnell carries the 24LC1025 from Microchip, which is a single I2C 1024Kbit serial EEPROM, which is quite appealing (memory: the more the merrier!).