Im not as worried about mapping the zones as I am about about understanding the concepts. Put another way, I want to understand when to expect a problem and how to adjust.
Part of the reason that I think I'm less worried about the mapping is that my norm is to peg my mid tones, because that's where my subjects are, rather than my shadows. Typically done with an incident meter.
That doesn't mean flare isn't ever a consideration.
Last weekend my wife and I went to Chimayo to see the church. They don't allow photography inside. So I got a long lens and set up on a tripod outside. Had it not been such a busy day, say mid-week, I would have walked up front with the incident meter, but of necessity I used my N90s with a 105mm lens and spot metered the alter as best I could.
I got close, but I believe the people in the doorway and the facade of the building contributed some flare in the lens and I got a reading that got me a bit less exposure than I was hoping for. I should have known that, or at least been able to guess that that would have bit me and adjusted properly.
Part of the reason I should have known is that I was planning on the the facade blowing out mostly, leaving just enough detail to see that I was looking in.