I think it all depends on the store.
Different managers handle their clearance items differently... I hit about 4-5 Wal-Marts on a semi-regular basis. One of them never marks things down, and when they do, it's like 5-10% off. Another knocks them down big time... case in point one store I go to, here's some of the deals I've gotten there over the past few years -
ROTS figures - $1.00 each (all kinds of characters)
ROTS mid size vehicles - $7.00 each (mostly Grievous Wheelbike)
VOTC figures - $2.00 each (mostly Han)
VSTC figures - $2.00 each (Han and Greedo)
SAGA2 figures - $2.50 each (all kinds of characters)
TAC figures - $3.00 each (TFU army builder galore)
TAC Max Rebo Band 5-figure sets - $4.00 each (both sets)
TAC Comic Packs - $3.50 each (mostly Wookiee/Clone wave)
GI JOE Comic Packs - $2.50 each (passed on those actually, all kinds of them)
I hit that Wal-Mart about once a week, and usually hit the clearance section first.