I have been using Linux full time since Summer 2004, but I had Linux installed on secondary hard drives going back to 1999, just to keep a toe in the water ;-)

My choice in using Linux, and Open Source Software in general, is about encouraging the creation of accessible resources. OSS puts tools into the hands of "the people". It's about creating a climate of plenty rather than one of scarcity. It's a concept that starts with software, but keeps going from there...

A nice little synopsis is here (with some links at the bottom to take you deeper): Closing the Knowledge Gap

But, ideology aside, there are more practical reasons. I was tired of having to constantly rebuild my system because of spyware, viruses and/or an operating system that just fell apart after a certain length of time (or became so sluggish and bloated that it was not worth trying to do anything practical on). There is, of course, a bit of an upstream swim in using Linux, so many things are made for Windows, but that's being worked around, and the reason I switched when I did, was because the software in Linux had matured to the point that I could accomplish everything I needed to with it. Some of the main pieces of the software that I use are also available with Windows, they are:

www.gimp.org An image manipulation program, similar to Photoshop (it can even open Photoshop files, as well as a whole host of other ones)

www.openoffice.org An office suite with everything you need for office work- word processing (including PDF publishing), spread sheet, presentaion design, etc. (it can open all the Word formats as well as WordPerfect and a bunch of others)

www.inkscape.org A vector graphics editor (along the lines of Illustrator)

www.blender3d.org This is a big one, described on the home page as: "Blender is the open source software for 3D modeling, animation, rendering, post-production, interactive creation and playback." But that's really the tip of a very large iceburg! What you can do with this thing is incredible. Some of my experiments are here:
Blender ZeD Part 1
Blender ZeD Part 2

gaim.sourceforge.net An instant message client that is capable of connecting to ICQ, MSN, Yahoo, Jabber, Gadu-Gadu, IRC, Groupwise, SILC, and more... It doesn't have all the "whistles and bells" of Messenger, but it's not bloated and invasive either ;-)

audacity.sourceforge.net A multitrack recording and mixing station with a wack of plugins (on Linux it uses LADSPA- a sound plugin framework that's pretty well utilized)

www.videolan.org A movie player that can read a remarkable range of video files- your search for codecs to play that file that someone sent you ends here- it'll play darn near anything.

But other programs that are only available for Linux, some have OSX ports, because it uses FreeBSD as it's base development platform, a very smart move. Here are some programs I use regularily:

www.kde.org My desktop- Linux is built in such a way that the underlying operating system is seperate from the graphic interface, so you can run different desktops, I use KDE, but I could equally choose to run Gnome (www.gnome.org). You can see what my desktop looks like by checking out these snapshots:

My image block thing is dysfunctional, I'll put them back when I figure out why...

bluefish.openoffice.nl This is a really nice HTML/PHP/CSS editor, it's my main tool for website development/maintainance...

Evolution And this is my email client, but its way more- it's like Outlook, but evolved.

www.scribus.org.uk A desktop publishing tool that's great for doing posters, fliers, pamphlets, etc.

www.k3b.org A general purpose CD/DVD burning tool, it can assemble DVD and do a lot of transcoding (changing the encoding of video files) functions as well...

akregator.sourceforge.net My "news ticker" this is a little applet that lets me read RSS feeds from news sources around the net- great for skimming headlines from multliple sources, and you can follow links to the full story if something catches your eye...

www.xmms.org A basic media player, similar to Winamp, it can even load Winamp skins (older ones)

www.jahshaka.org A realtime video editting and effects suite- I'm just starting to get into this, but it's developing quickly and has quite an interesting direction...

This is just a taste. I update these programs regularily (I run my update client weekly) from repositories all over the world, for free- no cracks or credit cards, just solid software tools developed by dedicated communities around the world...

Linux comes in a number of different flavours, these days I'm using Kubuntu, which is a version of Ubuntu . Another distro that has some fantastic multimedia capabilities is Dynebolic ...

I will continue with this, but this should give you some food for thought...