Hi ! It depends upon the level of testing you want to do and env. in which you are workiing. "When enough is enough" concept should be kept in mind because exhaustive testing is not practicaly possible. I mean we iterate a test case once and after the errors are fixed 2nd iteration is done. If you are working in a qaulity env. the iteration should not exceed 3 at the max. 
Also don't write separate test cases for all the valid / input entries for a particular field.
EX:
If textfield "ABC" should accpet excatly 5 lowercase alphabets then
Course of action should contain : Enter an invalid entry in "ABC" textfield
Input data spec. should contain " Enter "aaaaaaaa" in "ABC" textfield

And also texecute this acse for many invalid cases BLANK, "SASASASA", "%%^&^" etc. without specifying them in the test case or at the max. u can  provide sum e.g along with invalid entry word in course of action column.

If it fails when an input not specified in Input data spec. then specify it in Remarks column.

When you upload this bug in bugzilla / test director etc. you can specify exact number of steps......

Again if there are bugs even in 3rd iteration it is not much you can do dear...... u have to proceed toward 4th iteration (Screw the Developers).  Hope I am clear....

Regards,
SAurabh Garg