How do I get data out from the "Collect data from user" task that a workflow creates? So far my attempts have been failures.
The right way to use the variable "collect" is to, when using the lookup window (like when you are trying to update or delete an item), you should point to the Tasks List (normally it appears like "Association: Tasks List"), and, in the "Find the List Item" section, you put on the first field the value "ID" and on the second the variable with the numeric value.
It should return the workflow task with the data collected from the user, along with the custom fields you may want to access.
SharePoint indeed gives this warning, but even if it finds multiple items, it returns only the first one found, so it's not exactly an error.