I have always assumed that having so many distributions hurts Linux but it wasn't until I played with several of them that I even developed a preference for desktop layouts and configurations. When I used Windows, I never questioned the green menu and the blue bar at the bottom and didn't even care to customize it. When I used Mac OS, I didn't try to put a classic menu on the top bar, or move that top bar to the bottom.
I finally see that distributions are different ways of looking at the world and until you try them for yourself, it is hard to see the advantages or uses for them. Linux has made me question the way I look at my software and customize it to my liking. But more importantly, it makes me question how much I am consuming someone else's ideas rather than producing my own. I thank every Linux distribution for that thought in my mind.
What have you learnt from using linux?
After using a fair amount of distributions, and using them for a variety of different purposes, this became apparent to me: You have a Linux kernel, and a bunch of userspace applications, and the distribution you pick has very little effect on how any of this works in the long term. There's some small tweaks to the package management system, and the default applications, and ultimately it all has next to no effect on what your system can or can't do. Linux is Linux no matter how you slice it.