This seems to be hiding from many people,... :)
Excerpt from the README:
<blockquote>
If you'd like to play with a subset of your Library, you can click on the playlist
selector [picture]. Then choose any of your playlists.
</blockquote>
This should work with device playlists, radio tuner playlists, and audio CD playlists as well as user playlists. Some testing shows me that is not the case, however. I wonder if these are not properly implemented.

I have done some fiddling… with genres, and the best way to play with a genre for now is to make a smart playlist in iTunes, then restart the widget and select that playlist.

Thanks for all the kind words, everyone! (It's why I do it) More

OK, one star was probably a bit unfair, but I did have to hack the widget to make it work at all. After I did that, I found the game quite entertaining. I have a bug report and some suggestions (I don't like the forums because I'm sick of registering everything separately on the net, I want to use my Konfab account on the entire site). The bug is the clue button adding "by X" in the text field multiple times. My suggestions:
1) Allowing the library to be filtered and saving t…he filter to the highscore would give users the ability to customize the game queries. This would help a collector of 10000 songs brag about how well s/he knows e.g. Tatu instead of feeling perpetually inadequate.
2) The game shouldn't fail the round if only one or a couple of the words in the song title are given (it could give a penalty though). For instance, a specific mix of a song will fail unless you know exactly how to spell it. The words "the", "a" and "an" shouldn't have to matter at all. More

I second Xander. Without a function like that, I'm completely unable to run this widget, because my primary system language isn't English and therefore the name of my primary iTunes library isn't "Library".

Hey, a very fun widget, it works and looks great. I just have one request. Is it possible to have it play from other sources than the main library? i.e. Specific playlists and/or an iPod? I have all my songs on my iPod, so it's not so much fun with the few songs in my library.

It's very fun.
But Can't input 2bites characters!! I'm Japanese....
I'm glad if you make it can use in Japanese.

In addition, it's better that questions can be selected not only playlists but also genre.