A comment at Prof-like Substance caught my eye.
You called yourself a PI? What's with all these biomedical people referring to a professor as a PI? In some fields a professor is a professor. An academic title is more dignified than an administrative acronym.
I have a simple poll. Please select the equation that best summarizes your view of the relative status of the honorifics of "Professor", "Doctor" and "PI". For this purpose assume we're using the generic Professor to refer to all professorial ranks, not the specific for "Full Professor". PI, as you are answering the poll, means whatever you think it means.
In the comments you might as well expand on the rationale here.
The best I can come up with is that the smaller the group which can rightfully use the title, the better. Reflecting on this, however, it is clear to me that your definition of a PI is critical here. I tend to use Principal Investigator (sometimes Principle Investigator..YHN says meh) to mean someone who has written an application that has successfully garnered research funding. But then what do we call a n00b Asst Prof without major funding who nevertheless heads a research group? I'd probably call her a PI too, particularly if she was actively applying and otherwise giving every indication of being a person who would soon head up a major research award. A near-retirement graybeard who had pottered away without major funding for an entire career? Umm.... dang. Definitions are complicated. Help me out in the comments, eh?