Run 3 programs in DEV/TEST/PROD environments while running an incremental backup while editing an error report.. things can get sitcky not to mention you're running an email and RemedyForce.. i'd say a good amount is 16GB
I wouldn't sweat it beyond ease of use. I code on a used corporate ThinkPad I picked up for $100. Is it slower than my other machines? Yeah, but it does it's job just fine.
Now monitors that tilt vertical, THAT is kind of handy.