I've been a member of mapmyrun.com when it was a simple java script page that let you map out runs and calculate the milage. The site has grown since those early days (2006) adding a lot of new features, and therein lies the problem. Organizationally, the site is a bit messy, specific functions do not work as you would expect. For example, weight is a critical measure of progress, and I know the website tracks daily weight. But if you change your weight from one day to the next, and then revisit historical nutritional information, the current weight, rather than the historical weight is used to recalculate all nutritional goals. Critical - no; annoying - yes. Also, it appears, if you forget to record your weight for a period, there is no function I have been able to find to go back and change historical weight.
There are a lot of annoying little things like this that prevents me from giving the site more than three stars. I use it almost every day for very basic things, like recording runs and times and distances. Other functions of the website seem to go beyond their original calling, and have made the site a bit more convoluted than it needs to be.
On the plus side, they seem to be changing the website periodically so these issues may be solved as time goes on.
As of this writing (10/2015) MapMyRun.com is a work in progress.