I figured this was part of everyone's DNA by now, but, given a message I just received, apparently not. A reader who shall remain nameless wrote:

Is there any way to modify iTunes so that the program begins with no songs checked each time it is booted? Beyond the initial boot, I would like iTunes to behave exactly as it does; this is a feature I would prefer to have only when I click on the iTunes program.

And the answer is, of course, "Of course." Just hold down the Command key and click on the checkbox of a checked track. All tracks in that playlist (and this includes such major entries as Music, TV Shows, Audiobooks, and Ringtones) will be unchecked. When you quit iTunes, it remembers its checked-item state and so, when you next launch it, all unchecked items will remain so.

And--again, of course--when you Command-click on an unchecked box, all items in that list become checked.

Added value alert: For those who feel they've wasted a valuable 47 seconds reading this, here's a little something you might not have known (courtesy of Apple Discussion Forum visitor ed2345):

If you'd like to create a playlist that contains only unchecked songs in your iTunes library, do this.

Create a smart playlist that reads:

Playlist is Music

Make sure that Match Only Checked Items is enabled and close it. Give it the name All Checked.

Create a second smart playlist that reads:

Playlist is not All Checked

Genre is not Podcast

Playlist is not Movies

Playlist is not TV Shows

Playlist is not Audiobooks

Do not enable the Match Only Checked Items option and save this smart playlist as Unchecked. Now when you want to easily see what is and isn't checked, visit these two playlists.