I keep them. My Coach addiction is fairly new (about 1.5-2 years) and the earliest catalog that I know I have is last year's late summer/early fall. I'm sure I have older ones boxed up with some other junk as well.
I keep them discretely lining the shelves where I store my bags. I use them as reference for buying & selling to price and authenticate serial numbers.
I keep all the ones that have the purses I ownin them , just in case I need to remember the name or something . I like to relfect in the catologs about how I saw it in the catolog and tracked it down and bought it , I am like a Coach Purse Stalker !