Quickly Change OS X's Default Screenshot Format and Location
Just enter the following command (with the location set to where you want it:
defaults write com.apple.screencapture location ~/Screenshots
I put ~/Screenshots, which saves screenshots to a folder called (you guessed it!) "Screenshots" in my home directory. You can specify any directory you like. In fact, if you have a folder in mind and accessible in the Finder you can just drag it onto the Terminal window to automatically enter the path for you. This can save a bit of typing.
While we're at it, why not change the file type as well? OS X's screenshots naturally save in PNG format but you can change that to pretty much anything your
defaults write com.apple.screencapture type jpg
I used "jpg" as the example format, but you just need to swap in a different extension (e.g. pdf, tiff) if you like. When you're done with either or both commands, enter the following to reload your new settings:
That's it! Now you can enjoy your screenshots however and wherever you like.