My site started to get VERY slow loading pages (4+ seconds per page) and I decided to run a PHP profiler on it to find out what was going on.
After a lot of log digging I found that the PHP function in_array was being called tons of times and taking up over 50% of the load time of a page. When I looked at the call stack the origin was this plugin.
Whilst it is VERY cool and great for smaller sites the performance hit you take on larger sites makes it unusable unless you have very aggressive caching enabled.
Since I was only using it to exclude pages from the main header menu bar, I decided to take the HTML output generated and simply paste it as static code into the header.php so it is not generated every call.