I haven't done much on the inside, but I have used a similar decor as the tall one you built. I have only built 3 of the 12 floors in the building because I'm still working on the exterior.
I don't think we've got a mushroom biome within the boundaries of our world, definately not in the southwest/south/southeast anyway, apparently they are located within a bunch of ocean biomes, and our spawn is in the middle of some already.
Addictive yes. To be honest I don't dig anymore, that's the true life wasting element of the game, but if you're with a group of people doing a random fun dig then it's a bit ok. I have all the resources I need, pretty much.
All I ever do now is dig. In single player throughout today, I just dug a 2 wide by 3 high tunnel about 1450 block (at y=13.6) and didn't find a single diamond
I saw that on the chat what yesterday or the day before.
I know I didn't but that was odd that it was JUST the bed. (I had some idea on why but I wont go down that road)
It doesn't bother me, I thought it was funny! I'd prefer it if people left it alone but it's not like someone smashed my house to bits or anything. It was literally just the bed that went missing. The only other change was that Rob put 3 Melons in my 'kitchen' as he usually does every time I log off.