Oh, I'm going through the joys of renovation at the moment! Off the top of my head:
Ceiling tiles everywhere! Not only fugly but a fire hazard. Taken down to reveal that they were (mostly) stuck onto nice new plaster. The huge blobs of adhesive are refusing to budge so we will have to re-board and plaster almost all of the (perfectly good) ceilings.
Pulling up the flooring revealed (in one room): Lino > floor tiles > lino > lino > underlay > carpet. TAKE THE OLD STUFF OUT WHEN PUTTING SOMETHING NEW DOWN! Most of the other rooms were similar, if not as bad.
Terrible terrible thick flocked/foamy wallpaper. Hard enough to remove in itself, harder when painted over in gloss paint. It has taken me about 3 - 4 weeks to get the house stripped!
The porch is nice and looks lovely when the light is on in the evening. Trouble is, the only socket to turn the light on is IN THE HOUSE. Pretty rubbish when it's pitch black and you can't see the lock to open the front door!
The "conservatory". Oh god, the conservatory. It's actually more of a lean-to really. A complete 70's bodge, I have no idea how it's still standing.
After removing the awful homemade cupboards, the stud wall came away with it. It looked like MDF had been cut and placed in the space, no supporting timbers, basically not a wall at all! Discovered that the whole structure wasn't built in brick and rendered as expected. It's what only can be described as concrete slabs bolted together.
Considering it's been standing for 30-odd years, looks solid and hasn't fallen down thus far, we decided to keep it! (We did ask our structural engineer).
We've properly built stud walls, insulated and boarded the whole thing... it actually looks like a room now!
Oh, other than the fact that the main drain cover is in the middle of the room and we will have to make some kind of hatch with the new flooring. Why on earth you would build over that I have no idea.
Oh, and our staircase is completely illegal and doesn't meet building regs either. That was a nice surprise!