(NYT50) UNDATED -- Nov. 19, 2008 -- CIR-HOLIDAY-SHOP -- Getting ready shopping the day after Thanksgiving. Start with these simple facts: Retailers have to advertise their sales to motivate people to show up. These ads, often newspaper inserts, usually appear on Thanksgiving or the day before. But those inserts were printed weeks before they were folded into your paper. Enterprising deal hunters and loose-lipped workers have been known to obtain early copies of these ads to see what will be marked down and where. The Internet has made sharing this information wildly easier. (Illustration by Alex Eben Meyer/The New York Times)**ONLY FOR USE WITH STORY BY MARTY KATZ SLUGGED: CIR-HOLIDAY-SHOP. ALL OTHER USE PROHIBITED. EDITORIAL USE ONLY