Today's 6 mile run at a pace of 8:10/mile finished up in about 49:15ish. The significant part of the run wasn't the distance or the pace though. I made today's workout unique by infusing a short hill sprint about every .3 miles or so. I finished not only with the 6 miles done, but also about 20 hill sprints built into the run. Hill sprints or repeats are significant to workouts for a few reasons.
First, hamstring strength and flexibility is directly affected by the longer strides needed to cover an uphill sprint/repeat. It's a natural lengthening because the ground comes up quicker, hence you need to lengthen your stride to move up the hill.
Second, the hill work when done correctly, can a real benefit to proper running mechanics. Uphill running requires good form, with shoulders back and your hips under you, rather than slouching and letting your upper body lean and lead you.
Finally, mentally attacking hills, especially when tired, is a good way to get some toughness. This is not only beneficial to your workouts, but also your races when you are tired. The resiliency of a runner is evident by what they do not when they are fresh, but rather when they are wiped out.