When syncing a lead or changing it's owner, only real users and queues are accepted. We cannot use tokens.
We should be able to use any lookup field from SFDC that contains a user ID (so any SFDC lookup(user) field) to set the task, be that field on lead, contact or account.
A typical use case for this is that I get to know which account a new lead belongs to and I can attach the unconverted lead to this account in SFDC with a lookup(account) field. As a result, I can know the account owner, but as this is no standard field, I cannot use that info to assign the lead.
-Greg
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