I DID IT! After you install the extension I wrote, you'll have a field named "<DB ID>" for use in filenames and so on (note the space in "DB ID"). I use it to name files I sync to my Droid, for example -- my media player doesn't like Unicode, and some of my podcasts use Unicode names.
The only catch is that it uses your "Custom 1" field. If you're using that field for any other purpose, you'll want to hold off installing DBID, and let me know (posting here would be fine); I know of some workarounds, but I was too lazy to implement them. If you don't know what I'm talking about, odds are good that you don't need to worry about it; but if you are worried, ask here and it'll put some pressure on me to think about fixing it.
I've tested this well under MM4 on Windows XP, and used it for a long time under MM3. The install/uninstall is a little new, but it's very simple and seems to work well.
Click on this link to download a file
named "dbid.mmip" (it's in the "dbid" folder). Double-click on it to install -- MediaMonkey will open and pop up a dialog box asking whether you want to install it. (I provided an uninstall as well, if you decide for any reason you don't want it.)
If you don't want to install without knowing what's in it, use an unzip program to open up dbid.mmip; you'll find all the source. It's pretty simple.
What this does, technically and in short: it copies the "ID" field of the Songs table into the Custom1 field of the same table. It also modifies the MediaMonkey.ini file so that "Custom1" will be named "DB ID", and can be referred to by that name. Finally, it installs a "trigger" to maintain the table so that every mediamonkey track always has the correct value in that DB ID/Custom1 field.