TCO, as implied in the definition (Total Cost of Ownership), is an extremely complicated concept that depends on many, many things. You can't simply compare TCOs of various products, because in the end, TCO also depends on factors that are not always known. Thus, staring at TCOs is often meaningless.
In the local newsgroup about Holy Wars, the "TCO" has become the favorite weapon of the the Microsoft defenders. Short summary: They read jwz's "Linux is free only if your time has no value" comment, and keep babbling how cheap Windows will become in long run compared to UNIXes. You see, they say UNIX sysadmins need to be better taught, need more experience, and thus want more money for their services - while hiring any hairless monkey who passes the simple multiple-choice exam by guessing most is really cheap these days - Windows is so easy to administer.
Of course, in reality, the end result is quite different. First of all, there is no such thing as an "uneducated admin" - in any case, if you want to get things done properly, you need to hire an expert that actually understands the system, and in this respect Windows is not better than UNIXes. Also, there is the side of security - the TCO estimates don't take into account the losses due to security breaches and instability the companies are reluctant to publish, but as everyone knows, Windows is more insecure...
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The exclamation "TCO!", in sfnet.atk.sodat, means roughly "If we had been using something other than MS products, this would have been really cheap". Example: "Yeah, Word corrupted this document again, and the company has lost a lot of time and money when we need to deal with this sort of stuff. TCO! TCO!" or: "So you say the government estimated huge growth of license expenses due to the Microsoft's new licensing scheme? TCO! TCO!" =)
Also related is the mythical "Windows Next!" version, that supposedly fixes all bugs in current Windowses...
(Thanks to wick for mentioning the thing about security and stuff.)