Can SCAYT be on by default?

If you're using the latest version of CKEditor, it should be enabled by default. We can't actually turn it off yet, even if the spell checking buttons aren't selected, due to #817894: Support removePlugins setting to allow disabling CKEditor plugins.
Also see scayt_autoStartup setting for CKEditor. This is possible to override using an implementation of hook_wysiwyg_editor_settings_alter().

You can disable the scayt spellchecker and activate the browser internal ones like the one of Firefox using settings override.

I would not implement those hooks in WYSIWYG, but i think a good default would be very good for the reputation and spreading of WYSIWYG. Maybe it should be a submodule providing such defaults for each editor?

No need to change any config files when running under Wysiwyg. You can make Wysiwyg override the settings it sends to the editor without modifying any files in the CKEditor library or the module itself.

Create a new small modue (or reuse an existing custom one) and add this code to it. When enabled, it will override the scayt_autoStart setting for all editor instances.

function MYMODULE_wysiwyg_editor_settings_alter(&$settings, $context) {
  if($context['profile']->editor == 'ckeditor') {
    $settings['scayt_autoStartup'] = TRUE;
  }
}

EDIT: Fixed typo, thanks weekev!

If you're using the latest CKEditor version, this setting will already be TRUE by default so the above code won't make any difference. But if you're running an earler CKEditor version, it'll turn SCAYT on when the editor starts. (Note that the user can't toggle it themselves unless you also enable the SCAYT button under "Buttons and Plugins" on the profile settings.

Using CKEditor through Wysiwyg I was having no luck getting this custom module workaround working, then I went into admin/settings/wysiwyg and deleted the CKeditor profile I'd assigned, re-added it and re-enabled SCAYT and SC in the buttons prefs. The custom module now works like a switch. Thanks everybody for posting-

elizzle

For the record I was banging my head against a wall using the above code snippet in #4
When I discovered what appears to be a typo.

It should be...

<?php
function MYMODULE_wysiwyg_editor_settings_alter(&$settings, &$context) {
  if($context['profile']->editor == 'ckeditor') {
    $settings['scayt_autoStartup'] = TRUE;
  }
}
?>

- scayt_autoStart
+ scayt_autoStartup

Thanks everyone!

I had errors because $context wasn't being passed by reference so I dropped the & and everything was good.

I can confirm that this is the case, as described in comment#7, for wysiwyg version: 7.x-2.2 as well.

Fixed another typo in #4. It didn't really change anything, but $context isn't intended to be used by reference.