Previously I had recommended a not-free app called Glui for taking screenshots on Macs (in addition to the standard Command + Shift + 4 shortcut). Advantages to using Glui were and still are two-fold: (a) you can add arrows and text to your screen shot right in Glui and (b) you can connect your Dropbox account and, with one click, upload the image to Dropbox and get the URL copied to your clipboard. But I have since realized two things that have drastically improved the Command + Shift + 4 method.
The first thing I realized is that, as this Lifehacker post describes, you can easily change the destination that Command + Shift + 4 saves your screenshots, as well as the file foramt it saves them as.
The second thing I realized is that with my Logitech G602 mouse I can program the keyboard combination Command + Shift + 4 to any of the 8 spare buttons. So now I have the G11 button hit Command + Shift + 4 for me. I drag and select the screenshot I want, click, and done, it’s in my ~/Pictures directory. No menus, no new windows to close. Kind of feeling silly that I didn’t figure it out before.