For new photos imported into Lightroom 4 the Distance metadata does not show up even though I have it set to show up in my Metadata panel. For photos imported with LR3 the distance metadata still shows up.
I actually use that field for work, not just curiosity. When I have a batch of photos of the same subject, I'd take a look at their subject distance to avoid checking focus for all of them. (My camera has some focusing problems.)