road runners: Accuracy of MapMyRun

My running partners have been using MapMyRun for several weeks to plot out raoutes and calcuate workout stats.  We seem to be pacing out a bit faster than we feel like we are running, e.g. I would have guessed I ran a +9:15 pace this morning and I came in at 8:52.  I know the calculator is working okay as I have checked it against other online calculators.  Has anyone else "become faster" since using MapMyRun?  Or, are my running partners and I just getting better?