Previously, the Command-Tab switcher would keep keep rotating the selection if you kept the keys held down on the keyboard, continuously wrapping it to the left edge after hitting the right. In Lion, the selection stop when it reaches the rightmost icon, waiting for you to lift your finger from the Tab key and pressing it again before wrapping to the left and continuing.
This has been done to bring the switcher more in compliance with Fitt’s law and make it easier to reach the last item in the switcher without having to be careful about it.
Not that the last item in the switcher holds as much importance in Lion as it did before. Where previously hidden apps were taken out of the order and moved to the rightmost position in the Command-Tab switcher, in Lion they are just moved one place to the right of the newly active application.
This is also a welcome change if you, like me, regularly hide apps and switch back to them. When I hide apps, it is not an indicator that I am done with it for now and will return to it later, and I am glad that the Command-Tab switcher now respects that (although I suppose it could be a change for the worse for those of you who liked the previous behaviour).