You misunderstood what the guy from Id was saying. The threaded renderer does give a performance increase on dual core systems but it was expected to give a greater increase on 4+ cores. This is shown in the results of numerous benchmarks of the window$ 1.2 client and in my own benchmarks of the 1.4 Linux client. If you have a dual core system and you aren't seeing a noticeable improvement then you weren't CPU limited to begin with. That's why people with high end c2d and c2q systems aren't seeing much of an increase.
According to id Software, this threaded renderer will shine on systems with more than two cores, so really just quad-core and octal-core systems (for now).