there are lots of reasons that Microsoft is where it is at these days and a little research will show you that they have been guilty of some pretty heavy handed manipulation in order to get their market share. OEM deals with manufacturers, buying and suppressing competition, manipulation of governments, etc. I would agree with you on IT in terms of the desktop. The other thing is that nobody owns linux and it is free so there is no way of tracking how much penetration they have on the desktop market. Every new PC is required to be sold with windows and is therefore counted as a Windows computer. They have no idea how many are then reformatted to run an alternative OS. Distrowatch can give you some pretty staggering numbers of how many downloads for each distribution are recorded.
Overall, linux is in the forefront of the IT world. Redhat is one of the fastest growing companies, a huge majority of the web is run on linux - Amazon, Google, Facebook, etc. A quick nmap of meritbadge.net reports that it is running an Apache server. Something like 90 out of the top 100 supercomputers are running linux. Banks, Wall Streek - NYSE and most of the other stock markets are all running on Linux. If you want to see some really cool stuff check out Weta Digital - they are the ones that did all the CGI for the Lord of the Rings, Avatar, and King Kong movies. They have over 900 servers with something like 40,000 processors and over 100 terrabytes of ram being used to process these effects. This is all done on linux and there is no MAC or Windows software in the world that can handle that type of system.
Gaming community -
http://www.playdeb.net/updates/ubuntu/11.10/ and
http://www.penguspy.com/#/All/free_and_commercial/open_closed/sort=1/view=1/limit=0 . There are tons of free alternatives to Adobe. Open source software is a different model than you are used to.
Professional support and Best Buy shouldnt even be used in the same sentence....dont get me started on Geek Squad. Redhat and Ubuntu offer paid support for their servers. Personally, i have never needed it and am a self taught hacker because i can use google. Linux has as good if not better support for the majority of hardware out there. I am the IT director for a windows company and I can tell you countless problems with XP and Windows 7 and driver conflicts, etc. That argument is pretty much a wash. Google HAM radio & Linux and you will probably find tons of applications. Most HAM people that I know are do it yourself types so linux would be right up their alley.
I think you will be pleasantly surprised with the performance of linux on your old computer.
No one can pass through life, any more than he can pass through a bit of country, without leaving tracks behind, and those tracks may often be helpful to those coming after him in finding their way. - Lord Baden-Powell