New Relic shows the token hook being called a lot
I wrote a tiny module to log all calls to the tokens hook, so that I'd have some sort of idea where the tokens were coming from:

&lt;?php

function token_logger_tokens($type, $tokens, array $data = array(), array $options = array()) {
  watchdog('token_logger', print_r($tokens, TRUE), array());
  // Activate to fill up your database fast!
  // watchdog('token_logger', print_r(debug_backtrace(FALSE, 20), TRUE), array());
}


Turns out this was mostly the file_entity module running image alt en title tags through tokens, so that they could be overridden with another pattern if so desired:

// file_entity.file.inc:279

$alt = variable_get('file_entity_alt', '[file:field_file_image_alt_text]');
$title = variable_get('file_entity_title', '[file:field_file_image_title_text]');
// a little further down the line in a loop
$output = token_replace($alt, array('file' =&gt; $file), $replace_options);
// a little further still
$output = token_replace($title, array('file' =&gt; $file), $replace_options);


That adds up to 2 calls to the token hook per file loaded. If you have a busy website with a fair amount of images, it adds up quickly. About 800 calls each time the homepage is loaded, specifically.

I think I'll patch the file_entity module to cut out tokens for the default option, and verify it makes a difference speed-wise.