Dwarves already get happiness from a good drink, and they get happiness from attending parties, so taverns are already in. Make a meeting room with some tables and chairs, maybe defined from a drinking well or whatever, store your alcohol in that room, there you go you've got a tavern.
Dwarves also get happiness from waterfalls, and I once experimenting with placing my statue garden there so that dwarves would spend a lot of time right next to said waterfall. Of course they'd make sure they drowned themselves every season or so as a sacrifice to the 'water god' or whatever..
I think 'happiness buildings' are already done, in that dwarves get happiness from various aesthetic things. 'Admiring a fine statue', 'admiring a fine door', or what-have-you. Dining rooms are the big 'happiness room' right now, making a huge difference if you've got a nice one.
Baths don't seem very dwarvish, but we can make pools. I've actually never made an artificial lake so I've no idea the benefits, but I bet they get happiness from them and I've heard, but could be wrong, they don't cause dwarves to drown.. so baths are pretty much already in the game too, if so.
I think the main difference with the original poster's idea ofhappiness buildings is adding entirely new behaviors branching off from the new types of rooms. Worshipping at temples, fighting in gladiatorial rings, bathing at baths, and I'm just not very sold on the need vs the development time.. at the end of the day we need our dwarves to work, it's not like in Black & White where we just want them to breed and maybe, occasionally, sometimes manage to actually cut down a tree or gather some grain inbetween begging you to do all the work for them.. in Dwarf Fortress, every time in which your dwarves are eating, drinking, or taking a break is when something isn't getting done, and you can't reach out with your Godly Hand and do it yourself. A lot of players think their dwarves are indisposed entirely too much already.
The contrived complications of dwarves taking part in gladiatorial fights, or praying at a temple, may get in the way of more reasonable complications and mess up the narrative. That said, if done right they might add to the narrative and be pretty cool. Nobles can waste their time with these extra activities with no harm to the efficiency of the fort, and dwarves can spend their break times taking part in same activities for greater benefit than just standing around.
I wouldn't be surprised if temples at least were added at some point. Eventually it will be necessary to continue creating a fantasy world that allows for all the classic fantasy story themes.
[ August 11, 2007: Message edited by: Stromko ]