My opinion of the line in the sand for software is... It depends on the nature of use, and who you are interfacing with.
Nature of use: If it ain't broke, don't fix it? That may be truier than belived. I know several older computer users that use Word Perfect - on 5 1/4 floppies. They are comfortable with their systems. They know what they are doing. There isn't ANY benefit for them to upgrade. So why change? By the way, they are running DOS 6.2 with Windows 3.11
Interfacing with whom: That forces us to upgrade at my work. Wanna talk pain! Once one piece of Novell software is upgraded, history shows me that others will follow. Our tracking software. Sometimes e-mail and others. We also had a case... last week, where w2k HAD to be upgraded to XP. The software we purchased was not supported for anything other than XP. Would it work with W2k? Yes. Would they give us support when it crashed, No!
You also have to consider who you will be dealing with and their compatabilities. It may not be a problem with W2K yet, but I feel its coming. I don't know if my "Word Perfect friends" could work with the rest of the world anymore. But, I love their view. Dos is fast on the old systems!
"In a world where you can be anything, be yourself." ~ unknown
"Fall in love with someone who deserves your heart. Not someone who plays with it. Will Smith