Some stuff isn't outing, unless under very specific circumstances, e.g. running.
However some stuff is, and it doesn't have to be ice-sculpture.
There was a nice MNer once whose posts I tended to notice because she had a nice turn of phrase and a pleasant online demeanour. Over the course of a few months on MN, I picked up her age, the age of her children, and the county she lived in.
And then, one day, she made a post in Chat and I realised that this complete stranger goes to a work colleague's tennis* class, just because she mentioned the tennis tournament their club ran the previous weekend.
So now, I also know where she is one night of the week every week, and I could go there, hang around, and follow her home, too.
I've been really careful to only talk about my own "hobby" ever since.
*Not actually tennis