Drupal: Update user field

gistfile1.php

# with Entity API

$user = user_load('uidXXX');
$obj = entity_metadata_wrapper('user', $user);
$obj->field_XXX = 'blah';
$obj->save();

# Other way

$existing = user_load('uidXXX');
$edit = (array) $existing;
$edit['field_XXX']['und'][0]['value'] = 'blah';
user_save($existing, $edit);