Let me start out by saying that I only have one Spyderco, a Spyderhawk.
The fact is that most (all?) Spyderco lockbacks have riveted pivots. There's no way to adjust the pivot tension or even take apart the knife. This, IMO, is a HUGE negative against Spyderco knives because I am a tinkerer.
The FRN used for the handles has a cheap feel to it, even compared to other Zytel-handled knives like CRKT's and Gerbers (I'm thinking EZ-Outs). Don't get me wrong though, I like how my Spyderhawk feels in the hand. It's just that it looks kind of cheesy.
Just one look at the Spyderco forum tells you that they're a company that's very much customer-oriented and actually listens to user input. I also admire Spyderco for their dedication to design, in terms of ergonomics and getting the most bang for the buck, even if it means sacrificing a bit in the handle material.
So to me, FRN Spydercos aren't pretty, but they're fine as users.