Hyperthreading question

In "The Wonderful World of Linux 2.6" by Joseph Pranevich, I read the following about hyperthreading: "Of course, a single processor that pretends to be two is still a single processor and performance won't really improve much." This is what I've though, but I've never been able to see for myself, as the P4 systems with hyperthreading that have crossed my path, were all built on faster motherboards/ with faster RAM, ect. than the ones without it. Am I more or less correct, or am I missing something? Purely out of interest Thanks Hans