I've been using apple off and on since gradeschool and I still can't find where things are on them.
And it's not the big things that take transition time it's the little things like open apple click = right click (I actually have to carry my own mouse to UVU so I don't have to deal with that), how to find programs you want (why isn't there a freaking start menu? Oh you're supposed to search for all your applications) that kind of stuff.
When I was a brand-new user last year, I did a little looking around and stumbled across a free program called Quicksilver.
It is the coolest program I've ever used on any platform, and the most intuitive:
http://en.wikipedia.org/wiki/Quicksilver_(software)
Using it is simple; mastering it is beyond me, so I just let it do what I need it to do.
When I open up my PowerBook lid, all I do is press Ctrl+Spacebar, and start typing the name of whatever-it-is I'm looking for. I don't use the vaunted OS X Dock. If I want Firefox, I type FI and Quicksilver notes that I've used a number of apps that start with FI, but use Firefox by far the most, so it gives me that as a suggested option. I press Return and viola!, my app is up and running.
I'd rather start apps with the keyboard than having to find and click them anyway (and especially on a laptop) so Quicksilver not only has served to change the way I do things, it has made my life so much easier that I've never learned any other way on OS X.
There are scads of HOWTO docs on how to get the most out of Quicksilver, but for my purposes, the main functionality is, itself, more than worth it.