Tip #1: Refreshing ID3 Tags
iTunes doesn't show filenames or the Key tag, so you'll have to use one of the common ID3 tag writing options in the Personalize/Preferences of MIK if you want to view your keys in iTunes. After you've analyzed your MP3 files, the ID3 tags must be refreshed before you can see the updated information. To do this, select all of the tracks in iTunes you had analyzed and right click on your selection. Choose Get info, then check one of the boxes that you don't plan on using and write something into the selected box, and then press OK. All of your key info will now show up in iTunes. DO NOT check the boxes next to comments, BPM, Artist, or any other tag that you are using. This will tell iTunes to replace any of those tags with what you write in the box. If you did this you have just erased the tags written by MIK and any other info in that tag, and you need to delete your MIK collections and start over.
(The following method doesn't seem to work for iTunes 10.0.1 on Windows) There is another method of updating I just heard about from one of our forum members (thanks Derek:) If you click on the File tab and then choose "Add to Library" and select your iTunes music folder, iTunes will rescan your entire collection.
Also, if you are using MIK for Mac 4.1 with the write key to comments option enabled, and iTunes 9 or later, you may need to delete any existing comments in iTunes prior to analyzing the files. This works similar to the refresh. Once you have selected your tracks, right click, choose Get info, and check the box next to the comments box. If you had already analyzed your files with MIK before doing this, they will need to be removed from MIK's collections and reanalyzed.