Russ asks,

What's my grade going to be if I don't do it?
The traditional response is to assign zeros to students who do not turn in a project or a homework assignment.  Some teachers and even entire schools are deciding that handing out zeros doesn't make sense.
Let's assume you're into standards-based grading and you're talking with a colleague about it - or better yet, you're giving a presentation to a group of teachers about SBG.  The infamous theme of grading responsibility comes out in the form of a question:

Even after points are taken out of the picture, how do we motivate students to complete their assignments/projects?
I've tried not grading homework, but Johnny still won't do it.  Now what?
Colleagues and audiences frown at responses such as "build a positive and caring relationship with Johnny" and "find out why he's not doing the homework."  Most of us agree that these are good ideas, but our audiences usually don't buy them.  What are the tips and tricks you're using to overcome the grading responsibility hurdle?  Leave 'em in the comments. 

EDIT: (5/18/11, 11:30AM CST)
There has been some confusion in the comments about the context of this post.  We can all assume that the tasks assigned are co-created by the student and teacher.  In other words, Johnny has been given choices on how he might demonstrate his understanding of [insert the required standard], but he later is not interested in doing it.   Now, what?  Beyond "building a positive and caring relationship" fluff talk, what practical strategies are teachers using to overcome this hurdle?