I notice alot of you have 4GB ram, i only have 2 and never noticed any slowdowns, what advantage would 4GB give you over 2GB ?
See for yourself - "The numbers speak for themselves. Increasing the RAM in your computer is by far the best performance boost you can do to your system. Even increasing the RAM in your computer to just 2GB makes an incredible difference over the factory stock amount of RAM, especially when running more than one application."
http://eshop.macsales.com/shop/apple/memory/iMac_Intel_Memory_Benchmarks
At $100 for a matched 4GB kit, you can't go wrong....