Well, I've got two plumbers coming tomorrow for estimates and a third calling me to set up an appt. I had to fight through a half dozen of them that won't even come out to my house without paying $50 or $60 for a service call to get an estimate. Just as well, I'll probably get a better bid from someone who actually wants the work.

I'm going to definitely ask for PEX. I know the jury's out on it, but I'm glad people here have good experience with it, and with copper being so expensive now, I'm willing to take the risk that resale dips slightly. The NSF International study puts my mind at ease a bit on the health aspects of PEX.

Re: freezing vs. corrosion, I can't say for certain which it is, but the pictures look a *lot* like the pictures in that PDF report from the Maryland state gov't. I can't rule out freezing, of course, but the lady across the street told me they had to replace all the copper in their kitchen, and she said they didn't let the pipes freeze, so I'm starting to think maybe it might be cheap/impure copper combined with something bad in our water supply. But I doubt I'll ever know the gospel truth on it. (This is municipal water, BTW.)

Re: legal options, I emailed a friend of mine who's a lawyer and he's going to go over the agreement I signed and see if the home inspector has any kind of obligation to do his job correctly. If not, I'll probably contact him and explain the situation and ask him to do the right thing and give me at least a partial refund. At the very least, I'd like him to know that he should actually check the pipes next time around, so maybe others don't have to deal with this.

No homeowner's warranty, unfortunately. My buyer's agent told me that they mostly exist as a sales gimmick, and that most of them have significant restrictions on which contractors you can use, what qualifies as a defect, etc. I'm sure there are exceptions but at the time no warranty was offered so I didn't get one.

That Maryland report is fascinating. If it is something in the water, PEX is probably cheaper than trying to get some kind of water treatment system to deal with the problem.

Matt, thanks for asking your dad about my problem. I still have the piece of ceiling that was painted over, and there are signs of the water damage on the other side. I can't say for certain when the painting happened (I know I didn't do it) versus when the water damage happened, but it certainly raises questions.

I really appreciate all of the advice and discussion here, folks. I have a lot more info to tackle this problem with now. I'll keep you posted how the estimate/repair process goes, and on any interactions with the inspector/agents/sellers that may come from this.