Update a form field value - conditional logic

Is there a way to make a form multi-user.  That is, if I roll out my form to a handful of field techs, is it possible for a field on the form to default to the current user?

If I understood your question correctly, you want to prepopulate some fields inside of your form based on some selection. It is not possible for the form to recognize the user automatically (when he access the form). However you can use conditional logic "Update a form field value" to prepopulate fields inside of your form based on some condition. 

I have made a demo form: http://form.jotformpro.com/form/51804056395962? 

Inside of my demo form I have set conditional logic to prepopulate text box fields based on selection inside of dropdown field.

Feel free to clone my form to take a closer look to my conditions.

http://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL 

More about conditional logic you can find in this articles:

http://www.jotform.com/help/57-Smart-Forms-Using-Conditional-Logic 

http://www.jotform.com/help/286-How-to-Populate-Field-with-a-Value-from-another-Field 

Hope this will help. Let us know if you need further assistance.