It depends on the manufacturer, model, and the store. Not to mention how slow sales have been before hand. I have seen some go for half off but most times its a manufacturer I wouldn't touch or a model I wouldn't want because its features are not up to my needs. If the model has been discontinued for a newer model then you may see a really good clearance sale of more than 50%.
Edit: if you are looking for a general laptop that has the typical standard cpu and IGP, like the 4500, then you should find some really good sales starting Black Friday and running through till Xmas.