I'm switching to a Mac after years of PC use, and don't know what to expect. Any tips?
Macs are pretty intuitive and user-friendly so I think you'll manage. If not, most of the basic stuff is just a Google search away. I don't know if it's still a thing with new iMacs, but you might need to manually enable right-clicking in your settings. A couple of amazing Mac OSX apps I always recommend: Clear (todo list), OmniFocus, Pixelmator, Mailbox, Sublime for programming. If you work with MS Office files a lot, save yourself the trouble of exporting files and just get Office for Mac.
Get a harddrive and partition it with Windows so you can have the nice hardware and slick OS of a Mac and all the shit you can do on a PC and not a Mac. App Recommendations: f.lux, as wonton says. Mailbox, if you have a relatively simple email situation and want to simple it up even more. Bartender is AMAZING for keeping your menu bar from getting crazy. Doubling wonton's question about what tasks you might want to optimize.