"The difference between theoretical performance and real-world performance on the CPU level is growing fast. On, say, a regular Xbox, you can get very large fractions of theoretical performance with not a whole lot of effort. The Playstation 2 was always a mess with the multiple processors on there, but the new generations, with Cell or the Xbox 360, make it much, much worse. They can quote these incredibly high numbers of giga-flops or tera-flops or whatever, but in reality, when you do a straightforward development process on them, they're significantly slower than a modern high-end PC.
It's only by doing significant architectural work that you can even have a chance of finding speed-ups to what the PC can do, let alone its theoretical performance. It's only through trivial, toy, or contrived applications that you can deliver the performance they claim." - John Carmack