When an application displays multiple toolbars on one line, it starts to look cluttered, especially if windows are not maximized. This is because each toolbar eats some width on its left to show its handle, and when there is not enough horizontal space, it eats some width on its right to show its extender.
There are two complementary solutions to reduce clutter:
First solution is to ship with toolbars locked by default. Most users do not move toolbars around, and those who do are probably sufficiently tech savy to unlock the toolbar to be able to move them.
Second solution is to go through applications and merge some of their toolbars. The next section lists a few applications which would look less cluttered if some of their toolbars were merged.
Note: this list is not exhaustive, I just ran a few of the applications I have installed on my machine.
Some applications would benefit from being able to align toolbar elements on the right. For example it has become a de-facto standard that search lineedit fields are right aligned. This is common in most web browsers and has started to spread in other applications (Finder or System Preferences on Mac OS X, Thunderbird, Evolution)