The Walker stuff isn't exactly top quality, but I did get about 2.5 years from my Walker muffler (IPD sport exhaust).

I bought some very cheap exhaust pipe from Advance Auto Parts just as a temporary solution to pass emissions after my other muffler fell apart. They are perhaps the lowest quality parts possible. The pipe is completely covered in rust, and not just a little surface rust. It will be rusted through in under a year. My Magnaflow muffler, on the other hand, is looking great. A stainless version would last even longer than my aluminized muffler.
--
forums.turbobricks.com