No GMK is right, flashing from ROM manager isn't permanent (i.e., its not actually on the recovery partition)
Notice when you enter the recovery, it looks like its flashing something...
I verified this when I installed CM6 nightly. I had the 18.104.22.168 'flashed', but after I updated to CM6 it was suddenly back to 22.214.171.124
Samsung Galaxy Nexus
Rogers Magic on AT&T
HTC Touch HD