I personally run openSUSE Linux full-time, and have only booted into Windows a few times in the past few years to run a program for installing firmware onto my Samsung Android phone.
I started trying to use Linux full-time around 2001. My reason for switching was probably one of the strangest (and most invalid) ones out there: I received a trial of a program that I wanted to learn for my job that required Windows >= 2000, and my computer only had Windows 98SE. Since I am indefatigably cheap, (see the name of this website) instead of upgrading Windows, I chose to install Linux and tried to run the program under Wine. Well, needless to say, it didn’t run under Wine either.
But I was sick of blue screens on Windows 98SE, and I kept using Linux from then on. Frankly, Linux on the desktop in that era was awful, especially on my machine, which had a SiS 6326 graphics card. The Linux driver for the SiS 6326 was dreadfully unstable, and during the long period of time that I continued to use Linux on that system, I ran into far more hard crashes and loss of work under the Xfree86 environment than I ever did with Windows 98SE. But the siren song of free software kept me in the game. 
Enter circa 2005, when I bought my first laptop, a very old and — you guessed it — cheap, IBM Thinkpad. Since it didn’t come with an OS, I naturally installed Linux on that laptop. Windows never did see the light of day on that machine. The Xfree86 (by then “Xorg”) stability issue was greatly improved on this laptop, due to a much more compatible video card. But desktop performance was still abysmally slow because, like old4570, although I do know how, I hate command line and text file settings configuration. Thus, I was continually searching for a desktop environment that would consume less RAM than a Windows 98 or 2000 system while still being easy to configure with point ‘n’ click GUI tools.
I got more than a year of constant use out of that old IBM Thinkpad. Around 2006, I started to worry about hard disk mechanical failure, and when I found a great deal on a new Dell B130 laptop, I jumped on it. It came with Windows XP, which almost completely eliminated the blue screen issues of the bygone Windows 9x days. Also, in those days I was still dependant on dialup internet service, since there was absolutely no other option available where I lived. Since that laptop came with a weird “soft” modem, controlled by software drivers instead of onboard hardware logic, I was forced to jump ship to Windows XP, due to a lack of modem drivers under Linux. I had minimal problems with Windows XP on that machine. I never even installed an antivirus system, but I meticulously maintained and monitored my system and used only reputable open source software for Windows, which left me with a lightweight and fast system. But then two things happened: First of all, Dell surprisingly released a Linux driver for the soft modem in my laptop. Second, one day when something happened to my printer, I went to a public computer to print a file on my USB flash drive. When I went back to my Windows XP laptop and inserted my USB flash drive, I immediately noticed that it infected my machine with a virus. I manually removed it and sanitized my machine, but that still left me really worried about security. The feeling that my data might be in risk of corruption or possibly even transmission to a criminal really unnerved me. So, I finally completely wiped Windows off that laptop and installed Linux again.
I have gone back and forth between several Linux distros for daily usage, and I have briefly tried countless distros. Many of the distros are small projects started by a nice guy with good intentions, but the creator usually burns out after a year or two and the distro disappears. Most of the other small distros that manage to keep going still suffer from a plethora of bugs and weird hacks, and the project usually doesn’t have enough manpower to properly maintain itself. Most of the small distros have one or two really unique, innovative features for a specific target audience, but suffer from lack of overall integration and fail to satisfy the needs of a large general audience. There are a few exceptions. Although I would never run it on a daily basis, Puppy Linux is an incredibly useful tool for testing and fixing broken systems, it’s blisteringly fast, and its hardware support is nothing short of incredible. I always keep a copy handy.
So for a good Linux distro with plenty of manpower that it stable, professionally developed and maintained, and suitable for daily use on the desktop, my personal preference is openSUSE. It is incredibly flexible, very professionally presented, extremely well maintained by many enthusiastic supporters and developers, and it doesn’t force a default desktop on its users. It has commercial support, its entire infrastructure is superb, and it’s here to stay for the long term. Its package manager is second to none for flexibility. It allows for new releases of software to be easily installed on top of a stable base system, or the user can opt for the Tumbleweed rolling release paradigm. OpenSUSE arguably has the best installer of any OS, and its YaST system configuration tool is unrivaled for the amount of system features that can be configured without munging around text config files and typing arcane commands in the terminal. It has very good multi-lingual support. It is very stable, uses minimal hardware resources, and is generally consistent from one release to another. SUSE Studio is the icing on the cake— it allows a common user to configure a custom, re-distributable openSUSE live desktop and installer ISO, essentially a point ‘n’ click distro creator. In general, with openSUSE I can just get work done and concentrate on the task at hand without messing around with my OS.
So that’s my personal Linux story.
I have a few other thoughts and observations about other distros that I would recommend or not recommend, but I won’t bore you further.