Right. But you can diminish the damage by using iTunes' Search field to look for a specific thing — Beatles, for example — and then do a mass check or uncheck with just the results. Even if you originally searched the main Music library, your actions only affect those items. When you return to the broad view, you see only those items have been changed.

Or you could pull things out into playlists and do it there.

If you have a lot of holiday music, and you also enjoy listening to your entire library on shuffle, unchecking all of the holiday music means you won't suddenly find yourself listening to Jingle Bells in July.

That's one of the many reasons I use the "uncheck/check all" technique.

Typically if I like enough songs from an album, I will buy the CD and rip it to iTunes uncompressed (AIFF). I can then play these tunes lossless in my music studio or on Airtunes to the house stereo with "high" fidelity.

OTOH, my iPod gets 192K AAC files that are checked when I hook up the iPod for synching. So my library has two versions of each song, the "native" AIFF which I can convert to whatever digital compression scheme comes down the pike (if I need to for some reason), and 192K version that I use for now on my iPod.

A couple of smart playlists makes toggling the check boxes quite simple as the article mentions.

You can make the Unchecked playlist a lot more easily by just doing

Playlist / is / Music AND
Playlist / is not / All Checked

That should do it!

(Btw, "Genre / is not / Podcast" could fail if you happen to have a podcast with a custom genre. "Podcast / is false" is better.)