About half of the grad students I know worked for some period (at least a year) between undergrad and graduate school. Folks who do more "theoretical" work tend to come right out of undergrad. If your study interest is more hands on, then things get a little more complicated.
Some international students in the physical sciences and engineering have only a theoretical background. Their grades are terrific, but when they go into the field or sit at a bench, they have no idea how to apply what they've learned. And then they go into industry and start at a somewhat higher level, with more responsibility, but less of an idea of how to make sure that the scientific stuff is done correctly in the field. A good field or methods course can help with this, of course, but there's no substitute for fixing problems on your own, with real-world complications.
I came to grad school with a decent gap after finishing undergrad. I'll admit that I had to work harder than the students who came straight from undergrad, because I had to retrieve or re-learn some of the material that other folks knew right away. And I know that a lot of people want to finish their education as soon as possible so that they can start making money and start a family.
In my case, I went right to work after I graduated for another reason. I didn't admit it to myself until later, but I just couldn't handle more education at that point. I came from a culture where I was supposed to go to college, so I did. I worked hard and I made honor roll most of the time because I was supposed to do that, too. It was only when I finished college that I really took a look at what I wanted to do. It took working for years for me to realize that I really did want to learn stuff for its own sake and that I was really interested in various contamination-related issues. When I got to grad school, I had a great time learning new stuff that explained some of the problems I ran into when I was in the industry, while some friends who went straight to grad school were starting to burn out.
To get back to the previous post, I don't think that taking time off before grad school has a significant impact on your chance of getting accepted and your success once there. However, if you were not a fantastic student as an undergrad, success in industry can help as long as you show capacity for scientific work. I applied to departments that valued so-called life experience (they wanted resumés and accepted non-academic references) and departments that only wanted to see the academic record (3 references from professors whose courses I took years ago? ugh). In my case, the former liked my application more and I did end up in one of those departments, so it all worked out.