I am coming from Remember the Milk and enjoyed the ability to put time estimates on tasks and save by day to see if I was over planning.
Love your program by the way!
I have recently been using Toodledo, which has this feature implemented. It provided a total of the estimated hours for the particular view that was being displayed, which was absolutely brilliant. It was very easy to check if my daily planned tasks were achievable. I have a workaround in Todo, which is to allocate a tag representing the estimated completion time (e.g. 0.25 hr, 0.5 hr, 1 hr etc) to each task, then I manually add them up to check. I am looking for a solution for my company which has this facility, and would definitely support Todo if it had this feature included.