A few things I noticed about the Warforged and its effect on the game:
- Food. Food is usually only a problem at low levels, and it is always a group problem, not hinging on a single character. If it really becomes a problem, chances are high that you are in some kind of outdoor enviroment, and want a Ranger or Druid with a lot of Survival ranks anyway, who happens to be able to support you, too.
- Poisons. Most the time, poisoned traps are a problem for the Rogue in the group. He scouts, and accidently triggers them - if he actually fails to detect and disable them. Unless the Warforged is also the group Rogue, no real problem.
There are some monsters that deal poison damage, but there aren't that many. Even in this case, the typical person to actually suffer from them are melee fighters, who have a good fortitude save, and thus a fair chance to ignore the effects, too.
At higher levels (read: Once Heroes Feast becomes available), poison is simply a non-issue. The Warforged doesn't need to eat the Feast for the poison immunity, but a single casting will supply all party members anyway, so no difference to the standard group.
- Breathing. There aren't many situations in which breathing becomes a problem. Some of them are related to poisonous gases, and lead us back to the immunity to poison. The main issue is certainly the problem of water.
There are two water scenarios in my experience: Water has a kind of blockade to reach a certain area, and Water as part of a combat encouter. The former is a problem for the whole party, and a single casting of Water Breathing is usually the best way to solve it - which can easily affect the whole party, so the warforged doesn't change the situation much.
Water as part of a combat encounter is another matter. The best solution would be Water Walk, unless you also have to fight underwater. Breathing and swimming are both the problem in this scenario, meaning that the Warforged still needs ranks in swim to be able to contribute effectively in combat, unless his opponents happen to stay at the ground of the water...
- Level Drain and Ability Damage/Drain
These are certainly the most interesting and useful immunities. But mostly because these effects are really nasty and, in my view (that you might not share) very unfair effects. Still, the cheapest way to reduce someones ability scores are Touch of Idiocy and Ray of Enfeeblement, which, if I am not mistaken, cause an enhancement penalty, not ability damage...
Level Drain is certainly a different matter, but Vampires and other drainers can still provide a challenge to the party and the Warforged, because they will try to ignore and evade him in favour of his living (and tasty) companions...
On top of that, Warforged suffer penalties to Wisdom and Charisma. Charisma is certainly not really that important for most 'forged, but Wisdom means a penalty to many effects that the Warforged unfortunately is not immune to, and especially the melee oriented Warforged will suffer even more, as his will saves will never be great...