Safari freezes on pinch-to-zoom in Lion
Not sure I like it, but I think it's by design.  I don't really use the zoom function, but occassionaly activate it by accident when srolling.  When you zoon in, it seems to remove all navigation functions other than scrolling or further zoom operations.  You need to zoom back out in order to get it all back, however due to either inertia or some other feature it's possible for you to sort of bounce in again and zoom in a small amount again, making it seem unresponsive.  It's very subtle, especially as the text will render beatutifully.  So, in short, zoom out, check that you have really actually zoomed out all the way, then try again.