if you're a gamer and play commercial, store bought 3d games, linux isn't for you (unless your game runs in wine, but it's hit and miss, see
appdb.winehq.org)
if you need a desktop/laptop/netbook os to instant message/skype, use office suite, or browse the internet, linux is for you; the same if you are a business looking to cut licensing costs and get a great server or domain controller OS
also, if you actually fell for /g/'s "install gentoo", or actually installed slackware or arch, you are doing it wrong and you are doing the equiv. of judging windows by having used 3.1