I believe we experiece time dynamically where every past and/or current situation relates to and effects current and future conditions. Our experience of time is however based in our perceptive abilities leaving possiblitiy for endless interpretation of identical conditions. The past does indeed end when measured in reference to defined parameters but the effects resonate indefinitly. To gage the importance of the past is to quantify an event but generally speaking without past there can exist no present therfore invalidating the chance of future occurences and existence itself. Therfore I think the past matters to some great but as of yet undefined degree.