Well I cannot find anything that I would bother using for less than 4.2oz .
The minimum weight at the moment, with batt, is between 4.2 and 4.5oz.
Canon SD/Ixus, Casio S500/600, Pentax S5Z or WPi.
Soon we will have the Olympus 720SW, around 4.4oz with batt, waterproof to 9" and shock proof!
PMA, one of the largest photographic exibitions, will be on at the end of Feb, we may see something lighter then.