Agree, switch to Google for forum search. At minimum, adjust phpBB search settings like the common word threshold so that the most common and useful search terms do not get excluded.
Example: I want to know what I need to do to set up and use gpio. I enter "gpio" in forum search box and get "Information: The following words in your search query were ignored because they are too common words: gpio.
You must specify at least one word to search for. Each word must consist of at least 3 characters and must not contain more than 14 characters excluding wildcards."
If instead I enter "site:raspberrypi.org/phpbb3 gpio" into my browser I get a plethora of helpful results from this very forum.