The Anomaly Problem
Woah. In writing my first response to this, I was all prepared to argue that Neo was the anomaly. Mostly because of the Agents referring to him as such. After pouring over the Architect's speech during their meeting however, I realize that this is not the truth. Neo is not the systemic anomaly that the architect refers to.
The anomaly is what happens when a human becomes aware of the Matrix.
The Machines control the humans (bluepills) in the Matrix, by making them aware of the fact that they are part of the simulation. The only way they can do this with 99% acceptance is to give us a choice on a "nearly unconcious level": choose the Matrix, or reject it. Those who reject it, become aware of the simulation and become Awakened (redpills). These Awakened represent the 1% who cannot accept the Matrix or be controlled by the Machines. The Architect says that if these Awakened were left unchecked, they "would constitute an escalating probability of disaster." That is when Neo realizes exactly "why" he is supposed to save the human race.
The One is how the Machines control the 1%.
Using a Prophecy passed down by the 5th One at the beginning of the sixth cycle of the One, the Machines have put the freed humans on a path to follow this prophecy until the "return" of the One. And so, the humans wait, hoping for the day when the One returns to save humanity. This benefits the Machines, because the humans don't get it in their heads to start tearing apart the Matrix or take on kamikaze missions to take out the battery city with hovercraft, or resort to other crazy unpredictable behavior. All they have to do is wait and watch for their savior.
Then, when the Machines deem Zion to have become "full", they create the One (a thirty-forty year process, because Neo is "irrevocably human" and begin the process of destroying Zion.
Maybe the upgraded Agents refer to Neo as "the anomaly" because he is an Awakened, and therefore an anomaly. Maybe he was "the" anomaly they were sent to find.
I would also venture to say that the scenario of a savior would appeal most to humans, making it the most readily accepted form of control the Machines could use.
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The Smith Problem
Neo did not become the One until he died. During this critical process, he realized the extent to which he could control the Matrix. After this pivotal moment, his awareness of the Matrix was heightened immensely. Until Neo overwrote the Smith program, the Agent was just that: a program. When Neo overwrote him, a connection was created between Neo and Smith, whereby Smith gained Neo's heightened awareness of the Matrix. Every time Neo's powers progressed, so did Smith's.
In short, Smith was an accident, created by the One. That's why he was beyond the control of the Machines.
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D@mn , I wish I could make a living at this. Right or wrong, it's a lot of fun. . .