I make clones of my booted volumes all the time, but I make a point to ensure that no user-level applications are running when I do it.
That's what I used to do, back in the days when I was backing up my MacOS 8.6 ...
But when I went to OS X, I discovered to my dismay that "no user-level applications" wasn't nearly good enough. I was astonished at how much OS X does in the background, a lot of it with important files that really needed to be backed up. For a long time I made vain attempts to shut down more and more stuff, but it was becoming unwieldy to remember all the things that needed to be turned off, and increasingly problematic to remember to turn it all back on again after the backup. (At the least, you had to disconnect from the internet during the backup, because so many background processes are constantly updating files with information that becomes available online.)
I finally conceded that the only safe way to do it (and in practice the easiest way also) was to boot from a different volume. I never back up a running boot volume anymore.
Well, from the point of view of time, cloning by booting from a different volume is not the easiest way. The easiest way is to clone from the boot volume.
And, in my eight or so years of experience using Mac OS X's DU for cloning, up to Snow Leopard and now with Lion using CCC, cloning from the boot volume works just peachy fine. And I never bother to close down the internet connection either. Unlike Tacit, I don't bother to close down all the apps I've just been using. So what if Text Edit is open and so is Safari? Makes no difference.
After doing a clone, I always test it by booting from it for a test day. Never found a problem.
I'll happily and thankfully bow to Ganbustein if he can produce a good sized sample of competent Mac users who have had trouble cloning from the boot volume. Even better, if that sample was statistically significant. (Most samples aren't.)
But without some negative data on cloning from the boot volume, warnings against it are ... to put it politely ... just unsupported opinions. And they look really foolish to some of us empiricists who have been cloning from the boot drive for years without trouble.
Empirical data is what counts in everything -- wonderful theoretical opinions unsupported by empirical data are fun to contemplate and possibly the ringing bells for future improvements, but nothing to take seriously in their unsupported clothing.
As Ganbustein said elsewhere in these forums, let's get real.
