What have I gotten myself into???

Getting into trouble, as usual.

Well, I had a feeling, when I saw that the edges of the vinyl were curled up and blackened, there would be a nightmare hidden underneath.  I was right, and I literally did have a nightmare about it.  What was interesting was finding out just how many layers of flooring had rotted through.  There was the uppermost vinyl that was laid on top of an 1/8th inch underlayment, which was on top of another layer of vinyl (white with gray spots, except where water damaged was gray with white spots) which was laid directly on top of finished hardwood planks which were on top of wider tongue and groove subfloor planks.  Here is an artist's very hasty rendering:

1930-2011 Residential Flooring Cross-section

This is what it really looked like.

Now the worst is over, right?

I have a theory that old houses exist in some kind of alternate dimension where math doesn't work (Travis, back me up on this).  Apparently two boards with same dimensions as the originals don't equal the sum of two original boards.  Of course I didn't figure this out until I had already glued and nailed the new subfloor in place.  That is the least of my worries, however because overall the floor slopes by nearly an inch from end to end!  It's only a six foot room!  Well anyway, the plumber who came out today was neither surprised nor terribly concerned.  If you ever have this issue in a house you're working on, do not fear!  I can share with you some of the tips I've learned.  Which may or may not include shimming the tub with 3/4" OSB.  In this case, it does:

  
Stay tuned for the resolution of this problem!

Here is where I left things today:  

Decent progress, all things considered.

I also feel compelled to pass this on: if you ever set a toilet, choose wax ring/s sans plastic flange.  According to the plumber the wax can separate from the plastic over time and the seal will fail.  He says 9 out of 10 toilet leaks that he is called to fix are the result of this issue.