It is important - but, it's way overemphasized and other attributes concerned "speed" are ignored. Realistically, you can add 0.20 seconds to any reported time you hear outside of an NFL combine. If Joe Doe RB prospect claims an official 4.5, he's likely running a 4.7. Somewhere along the way, people got it in their heads that to be considered fast, you need to run faster than a 4.5. Then, someone decided 4.4 was the number. Then, someone decided 4.3 was the number. It became an inflated (or is it deflated?) stat. Plus, there are other interpretations of fast. A 40 time is not the only definition of speed. Look at Dexter McCluster. His 40 time wasn't all that impressive at the combine, but that dude is easily in the Top 5 of fastest college football players I've ever seen on the field - possibly, the fastest. I don't know what all his measurables are, but if that guy isn't considered fast, I don't know who should be.