Turbo Boost, is basically, the processors ability to OverClock itself to a higher clock speed in certain tasks when only a certain amount of CPU is being used.
What most folks commonly refer to as the "processors" is a physical chip package. "Turbo Boost" has more to do with having multiple cores (cpus) and using a fixed amount of energy. If only one processor core is being used then the "turbo boost" processors can shutdown the unused cores and use some of the power that would have been used to run them to clock the one remaining core at a higher speed.
So if you just run one program at a time. Start one, use it , finish/quit, start the next one . You can easily end up in a "Turbo Boost" situation. You can have mostly dormant applications to but "one at a time" drives home the point.
In contrast, if you have iTunes playing a song, while Spotlight indexes your hard disk, while time machine copies files to your time capsule , while playing some first person shooter game, then you will
not get speed boost. Many cores will be busy doing work and the power will have to be distributed to all of them. You'll finish the collective tasks faster because have multiple cores and get work done in parallel but the individual tasks may not finish quicker.
"Turbo Boost" is follow on to "Speed Step" where the individual core goes faster/slower depending on how much work is thrown at it (basically dynamic frequency scaling). Only it is also about power redistribution.
All the folks who think they need an 4/8 core CPU package or will just die .... won't see much of any "Turbo Boost". However, if have gobs of horsepower not really using, ironically , your individual thing will run faster.
On many of the cheesy synthetic benchmarks it is going to help alot. The benchmarks aren't very parallel and don't do much more than what a single core/CPU can do.