At least 2gb and oem only!
I had 1.25gb of omni hyperformance ram, switched to 1.25gb of oem apple ram and had a huge jump in xbench on the ram speed. I thought maybe I had bad omni ram but my xbench scores were much higher than any of my friends that actually had paired sticks of high end kingston and such, so having a raise in performance with the regular (albeit expensive buying it by itself) apple ram was very interesting indeed. Yes on the getting 2gb, because I don't do anything but average stuff like safari, ichat, itunes, iphoto, etc, use cocktail/diskwarrior/idefrag regularly and with dashboard disabled, my lappy is still always hungry for more ram (remember i have 1.25gb!). 2GB is honestly barely enough for even the average user especially with the oncoming of leopard which will be even more ram hungry (hopefully not as bad as vista which uses basically all of 2gb then has to swap the hd for ram) but these damn laptops don't hold enough these days and ram is expensive. In short (I ramble, sorry) 2GB of OEM Apple ram and you'll be fine (but not completely, thats what a tower is for) Get only 1gb and i assure you even with tiger, you'll be getting spinning candies of death with just 5 apps open. My friend brian has a core duo imac with 512mb, thought he had one of those faulty ones and after replacing it a few times, the people at the store basically told him he needed more ram because it ran like horse sh** with basically safari, itunes and ichat open! (Rambling again, i'll go now)