It's really not all that different from Windows when you get down to it. Apple and Microsoft have been stealing ideas off one another for so long, aside from some minor visual differences, the UI on Windows and Mac OS X are pretty much the same.
Keyboard shortcuts are virtually the same, just replace "Ctrl" with "Command"... On OS X you must explicitly quit from an app using the menu bar or Command-Q, it will not close just because you closed the last window. It is possible to alter the annoying inverted scrolling introduced with 10.7, though the easiest way to do it is actually to find a standard USB mouse, so the option appears in system preferences. Honestly, those are the only major differences I can think of. You just need to make sure not to let the visual differences throw you. The two are just not anywhere near as different as Apple would like you to believe with all the talk about the hundreds of new features they add every release (half of which are wallpaper files). Apple steals from Microsoft, Microsoft steals from Apple, and they both steal from lesser known companies as well.