Thanks to Mark, I now know how to capture the screen easily on my mac. Should have known this about day 3 in OS X, but necessity is the mother of knowledge, as they say…
First, from a terminal, change your preferences to capture jpgs:
defaults write com.apple.screencapture type jpg
Then, you can screen capture from any app (assuming you haven’t overwritten the default global shortcuts) by using cmd-shift-3 to capture the screen and cmd-shift-4 to capture a selection. If you choose selection, spacebar will capture the window your mouse cursor is over.
Screenshots are saved to the desktop.