Well, okay, technically it's the feast of the Archangels Michael, Gabriel, and Raphael. As for the sleeping late thing, I found it at this charming site:
There is a lovely old English tradition that one celebrates Michaelmas by sleeping as late as one wants. Here is an eighteenth-century verse commenting on this tradition:Alas, I didn't get to sleep late this morning. Our power went out during the night last night, and was out for about five hours. Just as we sleepily called the power company to see what was going on, all the lights came back on. But by then everyone was up, and we took advantage of the situation and got started on our school day early (well, early for us).
Nature requires five,
Custom requires seven;
Laziness takes nine,
And Michaelmas eleven.
If you travel around the blogs you'll find lots of creative ways to celebrate this feast day. Being a totally non-crafty sort of mom, I made use of Charlotte's coloring pages for today, and am cooking baked chicken breasts with sage and onions instead of a roast goose with sage and onions; goose might be traditional, but I've never cooked one, and really don't want to start a "St. Michael's Day Grease Fire" sort of tradition.
But I am going to remember the custom of sleeping in late on his feast day for next year! :)