According to a finding that I read about once, the perception of time's speed can be altered by temperature: when it's cold, time seems to go faster, and when it's warm time is perceived as going more slowly. This would go towards explaining those long summer days that last(ed) forever when we were all young, and also the fact that our body temperature drops as we get older, so that time would seem to speed up in accordance with body temp.
Thanks for posting about this-- always a fun topic.