(edited above because I accidentally said "TiBook" instead of "PowerBook" for the school... at the time the TiBook didn't exist
).
I think the important part about converting someone is the almost viral effect it can have. It's cumulative when you get someone to try a Mac and they really like it, then they tell someone else... etc. Apple's best sales I think still come from word of mouth (which is one of the major reasons I support the Apple Stores).
The company I got to switch was owned by a college friend of mine... we got into a conversation about computers (actually happened only a few months ago in January) and I told him I could save him money. I drew up a plan and 2 weeks later he hired me for 2 months as a consultant during which I upgraded his computers to iMacs (they were going to upgrade anyway), fired a number of incompetent people claiming to be "LAN Techs", put FreeBSD on his servers (they're still Dells, no need to upgrade the hardware), and personally interviewed and hired some admins I felt were considerably more capable than the ones that were downsized. The network still hasn't had any down time at all, and the number of problems reported to IT is down 90% (which is quite good considering a number of the employees requested training on MacOS X and said they were uncomfortable trying it). Oh, and the IT department is 1/3 the size it used to be (there were I believe 30 people in it... it's now run by 8 people... the savings there have been huge). Bah, I'm on a tangent, sorry. I still keep in touch with him of course (he paid me $30,000 for 2 months of work I volunteered to do for free, so I love the guy ;p). He told me recently he's noticed a lot of employees have been taking their work home on their own iBooks and TiBooks. He doesn't remember anyone having a Mac laptop before the change. Oh, he has a TiBook now too, and an iMac for his kitchen (don't ask)
Cheers,
Dak