Cannot use tokens to populate name fields

If you create a profile that uses the contact_name field, the maximum length of each name component is 20 characters. As a result, if you try to use a token to prepopulate a name component it always exceeds the max permitted length. For example, to populate the first name the token is [crm-core-contact:name-contact-name:component-given], which is 52 characters.

In addition, there appears to be no way to populate a field indicating who created the activity. If you want to know who updated a contact it seems that you should be able to use the activity participant field, which is an entity reference field. But if you put [current-user:uid] into the default value it throws an error.