When Music Note is checked, you can double click it to get a new selection of songs in the Now Playing list.
Otherwise the Music Note will keep filling up the Now Playing when Now Playing runs out of songs to play.
Script pick some good songs you have not heard for awhile. (Reads playhistory in MM)
Does it in a random order to make it more interesting.
Version 2.x allow adding some new songs to the list too.
Go to Tools - Scripts - Just Play Something Options to set how many if any.

# Songs. Script prefer recently added ones
New versions have and most likely will come here quite rapidly...
ChangeLog:
1.00 - 2.00 : Allow adding of some new songs, plus NonStop function
2.00 - 2.10 : Fix for unpredictable amount of songs selected (Thank you durden999uk)
2.10 - 2.20 : Fix for NonStop Off function
2.20 - 2.30 : Clean-up and much better solution for NonStop. Now totally 'dead' when not in use.
2.30 - 2.40 : Now pick 10 songs, and the Music Note button is now a double clickable button.
2.40 - 2.50 : Better spread, and randomizing
2.50 - 2.60 : New Songs to add improved.
2.60 - 2.70 : Double Click works first go now, plus the script got a lot lazier.
2.70 - 2.80 : More new songs as the script now prefer higher rated new songs.
2.80 - 2.8a : Made it pick one top rated new song at each load.
Fixed link to script 14 July 2014
Thank you paulmt & durden999uk for keeping me going!
Will have to sit back and enjoy the music for a bit and see if it's alright now...
Current Button Functions are;
1 Click = Turn on/off Non-Stop. Load songs when no more songs are lined up in Now Playing.
2 Click = Off then On within a second means load a new selection of songs
Install Script Open zip, and just double click the install file.
Script works best if you have at least a good few weeks of play history, and have played a fair good amount of songs in MediaMonkey.
It also helps if you have rated your songs fairly well, but that is not really a must. Script works with non-rated collections too.
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Only get to see a text file when you double click install file?
Try resetting vbs script behaviour to normal by
Start - Run and write
CScript //H:WScript
and hit OK
Many thanks to paulmt for testing this.
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The script ignore New Songs (never played) being rated between 0.0 and 1.5 Star, but it include Not Rated. If you're out of never played ones, it will pick some that you've only played once.