Here is a quick and easy Terminal command that will tell you what songs came from EMI:
mdfind -onlyin ~/Music/iTunes/iTunes Music
"kMDItemCopyright == '*Emi*' kMDItemCodecs == '*protected*' "
For more metadata fun, try the mdls command. A good example is:
find . -name *.m4p -exec mdls -name "kMDItemCopyright" {} ;
Note that all the labels owned by EMI are probably going to have the same no-DRM deal, so you'll need to run this command for all those labels. Luckily Wikipedia has a list.
[robg adds:If you want to send the output to a text file, just append > ~/Desktop/myEMI.txt to the end of the above command. If your music is stored in a non-standard location, you'll also need to edit the path in the command.
In the above-linked PR piece, Apple promises that "iTunes will also offer customers a simple, one-click option to easily upgrade their entire library of all previously purchased EMI content to the higher quality DRM-free format for 30 cents a song." However, I'm not sure the process will show you your EMI-sourced songs first, or let you optionally upgrade only some of the songs (via checkboxes, perhaps?). In any event, if you're curious as to how many EMI tracks you presently own, this is a good way to find them in anticipation of the new deal's May start.]

