its always nice to have lots of ram in your system, as it is a cheap upgrade and gives your system a big speed boost.
But if your like me and do a lot of gaming on the pc you no games eat memory for breakfast, so anything over 2gb is great.
Thats were the problem starts if your OS is windows xp or earlier it will only recognise ram up to 2 gb, and when you try to put more into the system. It will not be recognised by the OS, and in some cases slow it down. now if you are using an OS which is true 64bit like vista or other open source ones like linux etc. You can use as much ram as you want.