The Firefox keyword-shortcut for Drupal's API site breaks Evernote!
An unexpected error occurred while synchronizing with the Evernote service. The cause is listed below. Check to make sure your computer and network are operating properly. To resolve this error consider exporting any unsyncronized notes then permanently delete the problematic items from Evernote. If the problem persists see "Technical Support" under the "Help" menu.
The note 'Note title here' could not be synced. The content is not valid.
After first making sure there were no weird characters, i started deleting parts of the note until it allowed sync. This is the problematic line, from the excerpt below: http://api.drupal.org/api/search/7/%s <-- that is the content that is not valid. Silly Evernote.
Tip: easier access to Drupal APIs in firefox
Drupal 7 API Search
Go to the Drupal 7 API page and search for the search term. If you've hit on an exact function, variable, or filename you will go directly to it's page