Add to Xion Playlist is not showing for me in explorer on windows 7 Ultimate x64, just thought i would mention it hope its not been brought up before for this build if it has then just ignore me or tell me to shut up.
In Windows 7, just associating the file type within Xion isn't enough
Right click on a file (such as a .mp3), choosing Open With, and then 'Choose Default Program'
Choose Xion from the list that's displayed. Its a user choice thing in Windows 7. Applications aren't allowed to force an association any more, they're just allowed to register that they can handle the file types.
Once you've done this, the Add to Xion Playlist should work.
Alternatively it will always show up if you right click on a folder.
If its still not showing up, open Configure Xion, go to the File Types tab and check and uncheck the 'Integrate Xion into Explorer's context menu'