There have been a few posts on these and related topics but nothing comprehensive. It seems to me that Linux is a great deal in terms of cost and its functionality is getting better everyday. It would be nice to have a compilation of important/useful information for those that are interested in making the switch.
Q: What is Linux?
A: See Linux on the wiki: link.
Q: How come there are so many Linux operating systems out there?
A: They are all Linux distributions that are based on a common core set of programs.
Q: What is a Linux distribution?
A: See Linux distribution on the wiki: link.
Q: What Linux distributions are out there?
A: See the list of Linux distributions on the wiki: link. A more comprehensive list is available on LWN. DistroWatch tries to track the more popular Linux distributions. See a short list in the quick summary.
Q: Which distribution is right for me?
A: Perhaps the best way to find out is to try some of them and decide for yourself. A comparison of Linux distributions is available on the wiki. The Linux Distribution Chooser can provide you with a good starting guess. In addition, you should try LiveCD for those distributions that provide one. A list of available LiveCDs can be found here. Also see this thread.
Q: Will it work on my PC/desktop/laptop/notebook?
A: If your hardware is mentioned on the Hardware Compatibility List, then it probably will.
Q: How can I get hold of a Linux distribution?
A: You can download ISO images and burn them to a CD/DVD, copy the CD/DVDs from a friend who already has them, buy CD/DVDs from retailers who sell them at a small cost (~$2/CD or DVD plus shipping) or buy a packaged retail distribution. If you are planning to download a Linux distribution, be aware that most distributions now have several CDs or a DVD which means that you will be downloading gigabytes of data. The nice way to do this is to use a BitTorrent client although many distributions will let you download directly from their website or a mirror. See the links in the quick summary.
Q: I now have CD/DVDs for a Linux distribution. Where can I get help installing it?
A: In this thread to start with. Also take a look at Linux For Newbies and Installing Linux. Some related threads: thread, thread, thread.
Q: Which filesystem should I use?
A: See the comparison of file systems on the wiki: link.
Q: What applications are available for Linux?
A: A large number of applications are available for various tasks. See these threads: thread, thread, thread, thread, thread. See details in the quick summary.
Q: Pointers to more resources?
A: See these links: thread, thread, thread
Q: Are there any other free operating systems?
A: Solaris is currently a free download from Sun. See this thread for details on how to get Solaris and development applications for Solaris. There are also several systems based on BSD Unix such as FreeBSD, NetBSD, etc. See details in the quick summary.