After completing the beginner lessons, you might still want to practice QWERTY a few minutes each day so you won't lose your QWERTY typing skills.
I found the above quote on colemak's page "Learn". I personally haven't touched QWERTY since I've switched. But if I do type in QWERTY a sentence or two on someone else's computer, I look at the keyboard, since I no longer remember the locations of many keys. So does anyone actually practices with QWERTY once in a while to not forget it?