SR Macbook Pro 4gb vs 2gb RAM - much diff?

[electric ant]

Hi
If you have upgraded your MBP to 4gb of ram how much faster in real terms is it?
also if you run photoshop, vmware fusion, handbrake etc is it much faster?
with 4gb ram kit being unde £100 im thinking i might treat myself for christmas

 

[electric ant]

I'd agree a 7200rpm hard drive is tempting but the hassle of opening up the MBP and the loss of warranty put me off somewhat. I also have a large external hard drive so space isn't a factor.
Has anyone had any experience of using vmware or parallels with 4gb of ram, I'm hoping it will be a bit speedier, sometimes I use photoshop in Mac OSX whilst working with files in windows too.
I think I'll probably take the plunge anyway and get 4gb as prices seem pretty good now to be honest.