All I remember is starting my degree (in 2003), and having never used a Mac before, having to sit down in front of one and get started. Everything was fine until the program I was in beachballed, and I realised that I had no idea of any shortcuts, and ctrl+alt+del evidently wasn't the one I needed. 😛
I picked it up very fast (which is a nod to the excellent operating system) and after a week or two was definitely finding it infinitely more pleasurable to use than Windows, and pretty much haven't looked back since.
The thing that was the first wow factor was probably the dock or the incredibly intuitive drag and drop stuff like installing and uninstalling programs. That or Expose, but I think I found out about that later. In fact, a guy at uni who had been using Macs and OSX for several years was all "What the hell was that?!" when I hit F9, which amused me. He wasn't really a "read the manual" kinda guy though. 😀