Yes, I'm addicted to the hobby. In most cases, having a fish tank starts out as a hobby. But sometimes, I feel as if I'm starting to become obsessed.
Fish are relatively inexpensive when compared to the costs of many other animals, and with so many varieties and types, it is easy to become obsessive about the hobby. At first, a 20 gallon tank is great, but then you want to keep more fish, so you look to purchase a bigger tank. Maybe a 30, or 55 gallon tank. But after a while, as your fish get bigger, and you get bored of the species you own, and you want to get a bigger, newer tank. With more fish. Or perhaps you want to keep the fish you own, but you want to try a different species that isn't compatible with your current fish. So you start a second tank with a different species.
And sometimes this is enough, but many of the hobby magazines talk about the adventures of fish breeding...which then of course may require some type of breeding tank. And then you want to keep some of the fish you breed, so you need a bigger tank to keep those fish, and the cycle starts all over again.
I recently read that the most popular fish tank sizes used to be the 20 - 30 gallon range. More and more, however, the 55 gallon has become the standard for many fishkeepers. And with all the options available in tank shapes and sizes, it makes it easier to fulfill your addictions.
In my opinion, it's a matter of how it effects your life and finances. If it is something you enjoy, and it doesn't interfere with the rest of your life too much, then enjoy!