Yes, I use linux, along with Mac OS X (my primary OS) and Windows 7. Regarding linux, I started with RedHat 6, then a RedHat clone (CentOS 6.4). However, RedHat and its clones are not as easy to use as Ubuntu and its clones, and they do not have as many apps in the repositories. More recently, I switched to Linux Mint 13 LTS 64-bit, which is based on Ubuntu. I use KDE 4.10 as my desktop environment.
Linux Mint/KDE is just as easy to use as Windows 7 or Mac OS X, and the OS and most apps are free. Linux, like OS X, has the added advantage of the command line, which is available simply by opening a terminal. I really enjoy using linux, and it is essential for some of my molecular modeling applications.
However, linux has some drawbacks, such as a lack of software that is equivalent to applications that I commonly use on the Mac or in Windows. For example, I have not found any scientific graphics and statistics software for linux that is as good or user friendly as programs such as GraphPad Prism, which is available for Mac and Windows. Because of this, I use Mac OS X most of the time, and I use linux for things like molecular dynamics simulations. I use Windows as little as possible, but sometimes it is unavoidable. If I were a gamer, I suppose I would use Windows quite a lot, at least for games, which are not as widely available for Mac or linux.