I love my Kate bags too. The all leather bags last forever, at least they seem too. The nylon are good quality for a nylon bag, but they do get beat up from normal every day wear, as do the straw ones.
You have to be very careful if you buy on ebay, these bags are very easy to counterfeit. Stick to department stores, outlets, or katespade.com. kate spade.com has a sample sale about 4 times a year and you can get better deals then even the outlets. Alot of these bags are limited runs, so you can get some really different things. I got a medium straw tote with a large cute pink ribbon for $87 dollars during the last sample sale and before a classic large red nylon for $100 the sale before that.