I like following and reporting the track numbers because I love the sport and because it is just one measure of true long speed. Key word there is "long" speed. It's nothing more than a factual assessment of straightline speed and nothing more.
I'll also be the first to tell you it's relevance to football is minimal. It is something you include in the evaluation but just one small piece of the overall puzzle. If two kids believed to be close in their abilities on the football field then the track speed can be a deal breaker...all coaches want to work with kids that have it.
Truth be told even 40s are not overly important. It is nice to have good 40 speed at corner or wide receiver because it demonstrates abilities on plays made down the field BUT 99% of the plays in football occur as a result from what happens in the first few yards which is why 10 and 20 yard splits are FAR more essential to football. Mark Ingram ran a 4.6 at the combine but he's one of the quickest players in last year's draft. He'll make a lot of the crucial 10-20 yard runs because he has that burst to do so. I'll take a 4.6 corner with a 1.5 10 yard split over a 4.3 corner w/ a 1.6 yard split any day of the week provided there are enough differences on the field. Believe it or not there are solid 4.6/4.7 corners all over the college game and a few in the NFL.
Athleticism, toughness, quickness, elusiveness, power...these are far better traits for a football player to possess than pure, straightline long speed. But pure, straightline long speed is an added bonus and shouldn't be entirely ignored.