Let's not hide flaws and say 1gb is sufficient when the N9 has shown that on boot system libraries and apps/services itself take up 700MB of RAM.
EDIT: I stand corrected... you have to use "top" to see the amount cached, for some reason it isn't implemented in free (or maybe if you use bash instead of bb).
BusyBox v1.21.1 (Debian 1.21.1power1+thumb0) built-in shell (ash) Enter 'help' for a list of built-in commands. ~ $ free total used free shared buffers Mem: 235252 229308 5944 0 2580 -/+ buffers: 226728 8524 Swap: 804856 86948 717908 ~ $
(long and comprehensive comparison of various phones' virtual keyboards)