Originally Posted by Nilpotent
There is a lot of ongoing debate on the android community about task killers (apps that kill running applications and clear some RAM). People who seems to know the android system say that android already can free RAM automatically and efficiently (apparently this is especially true for Gingerbread and Ice cream sandwich) so basically you want most of your RAM full because it means your apps are already running in the background and you can call them really quickly when you need them.
That being said, there may be a difference between theory and practice. I would not be surprised that there is a threshold of free RAM to optimize efficiency (but is that 3MB, 100MB or more, I've got no clue). If there is no threshold, then 512MB is more than enough for current applications and the limitation is only the CPU speed and input/output data transmission.
For me, lag appears generally when I've been using the phone for some time so I would go for some free RAM is not bad.
I had the same problem. I found the program RAM Manager Pro, it seems to help quite a bit, expecially the non-killable launcher setting (I hate waiting for the launcher to redraw when I exit an app). I use the setting "Balance - More Free Memory" most of the time. I've gone from an average of 15MB free RAM to and Average of 80MB Free RAM, and my Exhibit II is much more responsive from what I can tell.