Three times in the past three years I've bought a complete set
of rubber foot protectors for the wooden chairs that are slid
day in and day out on the tile floors.

UPDATE:
I picked up some of those felt pads as you guys had suggested:
http://www4.picturepush.com/photo/a/...g/13146927.jpg

So far, they've been working much better than did the rubber feet:
http://www1.picturepush.com/photo/a/...g/13146929.jpg

Thanks very much for your advice.