The problem with Razer is the overall QA / production quality. They have a few products that are really really good, for example Razer Deathadder is one of the best mice ever made and Razer Blackwidow is a very decent keyboard for the price, but your entire experience hangs on whether you get an item from a "good batch" or a bad one.
So I hear. I've never had any problems with them, but I've only had the one DeathAdder myself which, like you say, is fantastic.
Thats been running fine for about a year now, with pretty heavy punishment being lugged around in my laptop case with calculators, tape measures and pocket knives, etc. - I honestly expected it to be dead by now.
My brother has a Naga, which he also really likes, although I'd never buy one. They're a bit small for my humungous hands, and I'd never use all the other buttons. That's withstood similar punishment for about a year also.
Its strange, I hear a lot of hate on the internet about their QA, mostly aimed at the Mamba I've noticed, but I know a lot of people that use their headphones and keyboards (I know quite a few gamers who swear by their Lycosas, though I could never use one of those after owning this Filco) and have nothing but good to say about them. The only product I'd buy from Razer, save another DeathAdder if this one dies, would probably be a BlackWidow, primarily becuase of the reputation that they have, and the fact that they use MX Blues, which I'll probably end up getting regardless of what my next board is. Having said that, though, the smudgy finish is the reason I went Filco over Das, and will probably keep me from ever owning a BW, too.