In the next version of SmartPlaylist you will be able to filter songs by their iCloud status:
"no ☁" --> select only songs which are actually stored on your device
"only ☁" --> select only songs which are in the cloud (but not downloaded to your device)
"All" --> well, all.
If you don't use iTunes Match (like myself) you can simply hide this rule in Settings.
"☁" is also displayed in the list and detail view for songs, which are in the cloud.
Note: This feature will only be available with iOS 6.