g1smd - 2:45 pm on Jun 19, 2010 (gmt 0)
The google cache version of one of my index pages was 7 days old this morning, now it's dated May 1st.
I have seen that happen many times over the last few years. Google reverts to older data for a short while just before the latest crawl data appears. It is likely you'll show a brand new less-than-24hours-old cache date again in just a few days time.