I made the switch three weeks ago, been a windows user since Windows 3.1

On your scale, I'd say it was/is a "2" for me.
My first hurdle was to get over the basic fact that a window in OS X represents a document and not a application - closing the window doesn't terminate the application. The OS X way of handling applications and documents is more logical once you get your head around it.
My second hurdle is that in the Finder ( equivalent of the windows explorer) OS X doesn't differentiate folders from files, everything is sorted alphabetically despite the type. This is a bit stupid if you ask me, I've read in some forums that some long time MAC users name their folder with a underscore at the beginning to get them sorted to the top of the list.
My third hurdle is to reprogram my brain to use the command button ("apple key") instead of the control when typing keyboard short cuts (like cmd C, cmd X and cmd V). This is not a biggie, but sometimes annoying. But I guess that's what you get after 15-or-so years on a Windows PC
My forth hurdle is to get used to the way the different OS's renders text on screen (TrueType Fonts). Mac OS X has a "softer" rendering than the razor sharp Windows rendering. Not a problem, just something to get used to...
It's so refreshing and stress free to have a computer and OS that's been maximized for each other: No dodginess because of ill written and badly implemented code, no crashes because of bad drivers and dll's - this is something the guys over at MS can only dream of, as long as Windows is on a "open" hardware platform the users will suffer...
All in all though, I LOVE my new MacBook Pro and OS X! Like someone else said, Windows didn't do it for me anymore and I grew sick and tired of it. I've got a kick out of learning everything from the ground up once more. I'm eagerly awaiting the new and forthcoming Snow Leopard, I'm in for the long run!
