I believe that the only reason dual boot was possible, was because the 2.2 alpha was installed only to the SD card.
But here is what I do.
1) Boot xRecovery
2) Go to backup/restore
3) Choose Backup and wait for the backup to complete
4) On your SD Card, locate to xrecovery/backup and rename your backup to something you will remember.
5) Now you can wipe the phone and install whichever other ROM you want.
Setup your new ROM with all your contacts, apps, etc.
6) When you want to go back to your original ROM that you had in the first place, follow steps 1 to 4 above to backup your new ROM
7) Then wipe your phone in xrecovery again, and go to backup/restore, choose restore, and choose the folder you backed up earlier
8) Now your phone will be back to the way it was before you wiped it in the first place.
That is what I do and its very quick, and easy to do