You asketh and I supply. Taken from the Sitrus Berry page(?) here:
"Restores 25% max HP when the holder of this item is at 50% HP or less. One-time use. Provides a one-time 60 power Psychic attack when a Pokemon holding this item uses Natural Gift."
So regardless of any prior damage, Sitrus Berry will activate after Belly Drum no matter what. Pickup at the very least has an extremely rare chance of use. Again, to quote the site's description "In single battles, if a one-time use item, such as Berries or gems, is consumed by your opponent, a Pokemon with Pickup gains the used item if they are not already holding one." So maybe ya net a an extra berry or gem if you're lucky, i dunno :P i have no opposition to the extra bulk, i didn't catch that when i was scrapping together the EVs, so that was a nice catch. so yeah, even if the possibilities are slim, pickup is a tiny bit better than gluttony. i didn't even know about that 'til i was half-way through with doing the analysis tbh :P
http://www.smogon.com/irc/ use mibbit, come to #neverused on synirc and #grammar(I know it sounds boring but its fun!)
when you get stronger upgrade to MIRC if you have windows or Colloquy if mac! come on, there are some cool people!