General ICU BreakIterator usage model

Hello,

ICU is planning on improving the BreakIterator performances.
There has been some optimization discussions but no concrete plans yet, 
hence I would like to get an idea on the most common usage model of 
ICU's BreakIterators in a real life application.

Here are some questions
* Are there frequent direction switching during an iteration? Or are 
BreakIterations ran in one direction until one end of the text has been 
reached.
* If possible I would like to have a brief description on the sequence 
of BreakIterator calls most commonly used
* What are the most critical BreakIterator APIs for your application?

Any feedbacks are appreciated.
Thanks.