I've been into magic for just over three years now (I think) and I started out with a couple of nasty bridge decks. I am, therefore, in a position to say that I can, in fact, feel the difference between those and a bicycle deck. I have only ever gone shopping for cards twice (thrice if you count the internet) The first time was for a brick of 12 bikes, which my friend and I split between us, and then again for a new brick as the first half ran out. I am still on that second brick. I once bought some shadow masters because I saw them and had an orgasm. It was my first and final fancy deck, because, nice though they are, they were black and so a little bit suspect, to my mind. I generally get through a single deck in a couple of months.
I should add that although I added to it, I do (slightly hypocritically) consider this thread a complete waste of time. It is one in which everybody is interested in speaking and no-one in listening. Furthermore I think that those of you with more than a few hundred decks are completely bananas, and sound like you're preparing yourselves for some sort of crazy card-apocalypse in which every reputable playing-card company has exploded.
The reason I mentioned how long I have been into magic for is because, I think that if you've been doing magic for years and (like me) you don't like to throw an old deck out, then I can understand you having quite a substantial number of decks... but four thousand? Really? *sighs*