I got 1gb,and well, its perfect for me, since i use a wide range of applications, and i can use a large system cache, not to mention the swap file being in the secondary hd, the performance boost thanks to this is awesome, and also, being able to have photoshop open, and then fire up need for speed hot pursuit 2 at 1024x768, then in half a race, someone logs into msn, so i alt tab and in less than 2 secs im chatting with that person, start browsing internet or uploading files via ftp, all without accessing too much the swap, or slowdowns (not to mention it takes no time to return to the game or to photoshop)
I just love my 1gb RAM equipped Sager
So...if you use lots of applications, go for 1024, if you only do gaming or browsing, maybe some work, 512 is the option.
Hope you get what you want
regards