David,
I had a Dr. at UCSF yesterday tell me that while there is no clinical evidence, she would suggest that I get the 
HPV vaccine after I recover from my treatment regimen.  There is some preliminary data that suggests that the Guardasil vaccine may help to strengthen the immune system against a reoccurence of an 
HPV induced cancer.
Also, have you ever bothered to determine if your p16+ test results really meant that you have 
HPV.  If so, did you go through the academic exercise of which strain of 
HPV that you have?
My wife says I am getting ahead of myself by thinking about this issue and that I should focus on getting through the treatment.  Just can't help myself.  I am, however, very grateful that I have settled on a course of treatment and that it will begin soon.
Thanks,