I see when developing a plugin, in some cases just get blank page, may be the reason could be:
- Syntax error
- Double define of a function
One way to see error that i tried, is to set $CFG->debug = true, but that is not all, there is need to set in .htaccess:
php_flag display_errors on
Do you know more ways to debug weird errors?

Comments
I use this in config.php
// performance and debugging //
// Uncomment this to get sql errors sent to the webserver error log.
// $CFG->dblogerror = true;
// put this to 2047 to get adodb error handling.
$CFG->debug = 2047;
but I never checked the code to see if this is necessary.
I also have used xdebug (http://www.xdebug.org/) to do profiling, but it does much more than that.