I wouldn't call them vouchers, but maybe that's local idiom, like they don't have ATM's in Pennsylvania.  Do you fill these out by hand?  Or are you using a different program from the one I have?  I find it odd that ProSeries has the W-4 and W-4P, but not the W-4V.  

In the early days of tax withholding on Social Security -- remember, it was tax-free before Reagan -- it was a hassle getting it started and then getting it stopped (like, when the client finally retired and dropped off the taxpayer rolls).  I'll believe you, if you say they're doing better now.