on my HP i have 4GB of RAM with pentium dual E2200 2.20GHz each

on my old computer i had over a GB of ram and i forget the processor lol

Well I recently switched to 1 GB
 

Well I recently switched to 1 GB. Previously I was using 512 DDR but I was having trouble playing some high resolution games. So I changed to 1 GB for optimal performance.

Around 8 months ago a few of the capacitors on my motherboard finally failed. I got probably 4-5 years out of that system. But, I went and rebuilt my PC. Upgraded the power supply, got a new motherboard, a high energy efficient dual-core cpu and 4 gigs of RAM. I went with 4 gigs because I had started using VMs on my computer and the 4 gigs helps keep things running smoothly with the VMs and my host OS.

I'll be putting a new web server online soon as well, with 12 gigs of RAM.

12 GB of RAM?!?! That's insane, man.

i am using 3 GB

With Windows 7 the optimal amount of RAM is 3 GB (if you have a dedicated video card). If you have an integrated video card I would say 4 GB for 64 bit systems and ...well, 3 GB for 32 bit systems (they can not handle more than that anyway)

I'm using 4GB in my Windows 7 - but not sure if Win7 can make use of all of it - or only 3 GB ? Anyone know ?

I am using 2GB for my windows xp. guess it is enough though.

guess RAM is also affected of what you're doing... gaming and photo editting would really need RAM and video card boost. for simple home use then for me 1 to 2GB is just enough for windows XP :)