I have 8GB RAM on my HP desktop and 6GB RAM on my Alienware m11x r3. It seems to do the job as I 90% of the time use them to browse the web and listen to music. Sometimes I do play games on them, and I haven't hit any brick walls with them.
This, in combination with their Core i7 processors makes them super-future proof. I'll probably be using them 5 years from now. :p