Using
this as my web/nfs server, media player (its connected to monitor and "tv" monitor), music player and a generic use pc to do anything I want. Serves great except it doesn't like flash much. But for that I have my "gaming" pc that runs windows and is only ever turned on when I am watching top gear/other flash videos or want to play some old game (the pc has very old specs now

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There are reasons to use linux, and there are reasons to use windows. Personally I love how linux can be configured to suite you, how if I want to do something, 98% of the time. it is faster for me to do it via a $TERM, without the need to wait for some gui to load, how you can change your window manager to anything you like. And most of what queen13 said.
Would probably agree on the speed, my box is just a 1.2ghz with 1gb of ram (maxed), and it handles everything outside ram/cpu heavy tasks (and even the letter is fine, just leave nice -15 and you can still go and do other things while its happening). Saying that, my box copes even with playing back 720p videos (after re-encoding them to remove heavy compression), have yet to test it out with 1080p streams, but have not had a chance to look for them.
The way I see it, some linux distros are just not as bloated as windows oses. If you spend time and can cut out lots of things that you do not need in windows, then chances are, performance would probably be quiet similar, or at least similar enough that a user would not notice, just with linux it is much easier to do and free.