I'm playing a game as iroquois right now. I have to see the longhouse does not get less useful as the game progresses. There are simply too many reasons to leave your forests standing. Right now I have about 60 gold from trade routes and I'm only spending 5 gold on roads to link up the few spots where the trees didn't connect. Not to mention that, my cavalry can go from one end of my empire to the other in 3 turns.
My starting area was a peninsula that had a lot of forests scattered about, with a hilly region to the north (germany) and a to the west a choke point leading into a huge area covered in forests. I put up three cities in my starting area, then rushed the forest area to the west to capture the city states there and establish some cities before the AIs could cut down the trees.
I'm combining the iroquois special ability, the mohawk warrior trait (which is preserved when you upgrade the unit) and the +33% home-field advantage in the tradition tree to maintain a super-bad-ass defense army.
This is my first game on King difficulty and none of the other civs have been able to make me lose ground in the west where all the trees are. Germany captured a city off of me once, but I hit them back hard, grabbing all of their iron cities and leaving them pretty much harmless.
tl;dr version: Iroquoise are pretty good, and the longhouse is awesome, you just have to be aggressive early on to get those forested areas before they get cut down.
I used The iroquois the other day and had a strong game mainly due to the Longhouse. Built trading posts and got hammers and money out of those forests. My only problem was with the trade routes. All my cities had touching borders yet it was not counting them as trade routes for some reason. When I finally build roads, it gave me the pop up that my cities are now connected through trade routes. Not sure why. Any ideas?