I'd recommend keeping the OEM memory until your Apple Care expires (stored safely away in the containers the new memory you plan to purchase to prevent ESD damage). That way, if you ever need to take it in, you won't risk loosing your memory upgrade (need to swap upgrades out before shipping the system back to Apple; other members have lost upgrades in the past by not doing this).
I know it's a PITA, but it's worth the effort not to loose expensive upgrades IMHO.