I'm dual-booting between Ubuntu and Windows XP. Ubuntu is a fork from Debian, so it gets a
lot of useful legacy packages, but I think it's starting to eclipse Debian in terms of popularity.
As for how well it works, I really only boot to Windows for Windows-specific applications that don't work with WINE and Journey to Rooted Hold - and I only reboot for JtRH because I'm too lazy to export all my data across to a second installation! Any open source applications you're already familiar with - Firefox/Opera, OpenOffice etc - will almost certainly be available. Firefox, OpenOffice and Gaim are installed by default, plus a decent number of Linux-specific apps to fill the rest of the gaps (email client, text editor etc.) Since most users don't program, it doesn't ship with any IDEs or compilers but there are loads available. Installing programs doesn't require compiling them - you can get precompiled binaries from the official repositories. A side effect of this is that installation is actually much easier on Linux than Windows, because it's totally standardised!
Security-wise, you get minor auto-updates for
all installed packages (not just those integrated with the operating system) daily or once every two days. They don't require reboots. There are no Linux viruses in the wild AFAIK, so it's as safe or safer than a Mac.
Hardware-wise, it will detect most or all of your devices out of the box, although there are a few things you may need to do manually. If it doesn't detect your printer (it didn't mine), adding it takes about two minutes from the System->
Printers dialog and it'll work from there. For legal reasons, a lot of audio and video codecs aren't shipped with the system, but you can install them the same way you would any other program. Ditto
some graphics drivers (nVidia and ATI) - but again, they can be installed the same way as any other program. Note that there are placeholder drivers installed by default - you won't be kicked to the console - but if you want to game, you'll need to install the official ones. I hear rumours about bad wireless compatibility, but I don't have a laptop so I can't confirm or deny them.
Community-wise, you won't want for tech support - the community is pretty friendly and responsive.
Freedom-wise, it's free as in speech and as in beer, although the company (Canonical) does make money selling specialty tech support and various other services. Also, they'll ship you a free CD if you ask for one.
In general, it needs a little setup but once you have it the way you want it, it's much better than Windows. At least for me - your mileage may vary.
If you're interested, here's my full setup:
Click here to view the secret text
×Text editor: gedit (default)
Archive manager: file-roller (default)
TeX editor: texmaker (default)
Image viewer: gThumb image viewer (default)
Comic viewer: Comix (my addition)
Image editing: GIMP (default)
Torrent client: Bittornado (non-default)
Browser: I switch between Firefox (default) and Opera (non-default) at random.
Email client: Thunderbird (non-default)
IM client: Gaim (default)
Word processor, spreadsheet, database, presentation-preparer: OpenOffice (default)
C/C++ programming: KDevelop (my addition)
Python programming: IDLE (my addition) and SPE (my addition)
Music player: AmaroK (non-default)
Sound editor: Audacity (my addition)
CD ripper: Sound Juicer (default)
CD burner: Serpentine (default)
Movie player: Totem (default)
Screensaver daemon: XScreensaver (non-default)
A word of warning if you're planning to upgrade to Vista: historically, Microsoft's installers have tended to overwrite the boot loader with one of their own. Which doesn't check for other operating systems. In practice, that means that if the trend has continued with Vista, you'd be better off installing it before playing with other operating systems, or after installing Vista you'll need to mess about a bit before being able to boot to Linux again.
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Stupidity kills.
Absolute stupidity
Kills absolutely.