Selected maybe 100-200 lines of text that had been indented in SSMS. Hit Shift+Tab to decrease the indent level. Nothing happened. Tried again - still nothing. Clicked the button to decrease the indent and the app hung for maybe 30 seconds. I didn't really stick around to wait for it to finish, just switched to a different app to do other work, then came back to repeat the process (it had been indented several times).
I don't know if that was due to the fact that it was commented out or just the reformatting involved, but it was slow enough to lose several minutes just to re-format my text.