I do believe Unix-based OSes are more stable I have been using linux for almost a year and have had very minor problems. Simple mistakes that anyone could have made.
However, compared to Windows the problems that I had were not always user designated problems. More along the line of programming. Windows 95 I actually found to be very stable. Windows 98 seemed to crash all the time with the blue screen of death, frustrating. Windows XP I have found has stolen a lot of ideals to increase stability from Unix-based systems. I'm not so sure if this started on Unix-Based systems, but the fact of when a program crashes and the whole operating system stays together. For instance a program crashes in XP it asks if you want to force it to stop running. In Gnome this is the same thing. Microsoft has gone around stealing ideals for along time... I guess it's not really stealing since linux is more open source and lieniant. However, you take an ideal to better your operating system from Microsoft and they will make sure it never even gets to the starting line. Don't get me wrong Windows XP crashes, too, it's not the users fault that he's typing in Word and his computer dies.
This frustration from crashing lead me to try Linux and it's working great I have not one complaint. If a Windows user is a little uneasy about switching you should do them a favor and get them one of the many Linux Live that run straight from a CD. No installation no harddrive needed.