From wikipedia on the brachiosaurus:
What on earth is the point of having a ridiculously long neck, if you cant raise it above your shoulders?
Not everything has a point. I guess that throws intelligent desing out the freakin window. That… and our apendix. 
I get a little laugh imagining some huge dinosaur trying to eat from the top of a tree and just passing out.
It would give the animal an extremely long reach in a horizontal direction. It would be able to feed from plants over a wide area without moving its very heavy body. This would save a lot of energy in gathering the huge quantity of food it needed to keep going.
This is a likely explanation for the long necks of some sauropods. However, despite the contention about blood supply, I wonder if it really applies to Brachiosaurus. The very long forelimbs certainly suggest an animal that was feeding by reaching upward, rather than horizontally.
I do not know the current thinking on what the articulation of the neck bones say about Brachiosaurus’s posture, but that could help answer the question.
If you read something that sounds silly on Wikipedia, it probably is.
I’ve read that brotosaurs are now believed to not have been able to raise their necks because the construction of their nweck bones prevented it. I’m not sure I believe it (or want to) – there have been reconstructions of sauropods ith necks raised, and the bones certainly didn’t prevent it in those cvases.
I’ve never heard anything about them being unable to pump blood up there. That seems fishy. After all, giraffes have long necks, and can raise their heads above their shoulders. This requires some tricky biomechanics, and a nifty blood vessel system called the reticulum mirabile that allows the giraffe to survive significant changes in blood pressure in its head. But it allows the giraffe to raise itas neck high and to bend it down t the ground (to drink water, for instance). I don’t see why sauropods couldn’t have had something similar.
There’s still a lot of debate about this (search through the DML archives on DinoMorph or sauropod neck, see esp. this thread http://dml.cmnh.org/2006Jan/msg00125.html). It seems unlikely that Brachiosaurus could have achieved the stereotypical “swan” position, but it seems like the general consensus is that it could have reached at least a 45 degree angle if it stretched. Unlike most sauropods, brachiosaurs had longer front limbs than hind limbs, so it’s a safe bet that at least this family fed off of high vegetation.
The heart thing is a seperate issue. I remember reading that someone calculated how big the heart would have to be to pump blood to the head, and it was pretty darn big, though not impossible given the size of the chest cavity. Others have suggested there may have been some sort of “secondary heart” in the neck, though to me that sounds a little too much like the old “second brain in the tail” fallacy…
Any rate, that illustration on Wikipedia is very current and reflects a pretty reasonable neck posture.
Just shooting from the hip as someone who keeps reading every new article I see on Dinosaurs and watching many specials on TV.
For every scientist that would support the concept of:
There is another scientist who theorizes the Long Neck Sauropods reaching high up to trees not accessible to lesser creatures.
Jim
WAG: With a long horizontal reach, a brachiosaurus could stay in marshy water, relatively safe, but still reach plants close to shore.
The foot structure of Brachiosaurus does not suggest it was semi-aquatic, contrary to earlier suppositions.