My suggestion is to display the exercises heart rate zones, using percentages and/or graphs. It is a very useful feature to assess the effort level. Most of the other web based fitness logs include this feature.
Well it already does, doesn't it? When you view your activity detail and look at the hr stats, there are three little buttons to let you select how you want to view it. It also changes the values on the graph. Although the graph looks pretty much the same, because whether its HR, % of Max or zone, the relations the same graphically.
I admit I'm dense sometimes and I've not seen how they implement this on other sites. So if there's more that can be shown better, let us know with some visuals.
I see what you mean, but I was rather referring to be able to see the actual time spent in each heart rate zone. I attach an image taken from the Polar PT as an example ( graph on the right)
