Usefulness of prior industry experience before entering grad school?
I sit on graduate admissions committees (in computer science, in the US), and I spent 4 years in industry before going to grad school.  I agree with others: Industry experience per se is not particularly attractive, unless it's directly related to your proposed area of study.  (Industry experience may be more attractive in more applied areas of CS; I'm a theoretician.)

But it depends on what you do while you're in industry.  Admissions committees are looking primarily for strong evidence of research potential — raw "wattage", intellectual maturity, independence, initiative, creativity, attention to detail, eagerness to fight with hard problems, and most importantly, real results.  Recommendation letters that specifically address those qualities, whether from academia or from industry, will increase your chances of admission.  If you just sit in your cubicle and competently produce the code that your manager asks for, not so much.

My industry experience was a point in my favor during my academic job hunt, but only a minor one.