From the link:
Some key points from the report (keep in mind this is specifically for the E6500 with the NVIDIA graphics option, but much of this likely applies to the E6400 and/or the Intel integrated graphics option):
1. The problem is NOT an overheating problem - the system simply does not overheat. It is due to premature and overly aggressive attempts at thermal control, invoked at what are NORMAL processor operating temperatures (65-80 Celsius), possibly due to faulty ACPI "passive cooling" parameter definitions and/or control methods.
2. The problem is substantially more pronounced when the system is docked.
3. The problem is aggravated somewhat by the use of dual monitors when docked as opposed to a single monitor.
4. Since the problem is all about temperature, the higher the surrounding ambient temperature in the room, the sooner and the greater the performance loss.
5. The symptoms are much more highly correlated to elevated NVIDIA GPU temperature than elevated CPU core temperatures.
Some miscellaneous corollaries:
1. Any blockage of air inlets or outlets (including, of course, dust) will aggravate the problem.
2. The reason people report shockingly high percent CPU utilization statistics when their system slows down is that the overall capacity of their processor is degraded by the throttling mechanisms. The same processes running on a CPU that is subsequently throttled necessarily will demand a higher percentage of the processor's remaining capacity.
3. The reason some folks report persistent slowness even after installing software to prevent CPU downclocking is that more than one throttling mechanism is in play here. In particular, Software-controlled Clock Modulation (also called On-Demand Clock Modulation) occurs in an almost completely invisible manner, as opposed to performance state changes (which are usually monitored by common utilities). Another often-invisible throttling mechanism is Dynamic FSB Frequency Switching (where the FSB frequency is slashed in half), though if you prevent performance state changes, that takes care of preventing this too (since it's part of state P3).
4. The reason there aren't more complaints (though many are accumulating these days) is that users who experience this problem simply have no way of knowing what the cause is and are likely to blame the wrong thing (Windows, recently installed software, cooling hardware, etc.). Untold masses may be adversely affected by this problem, but nearly all of them wouldn't know it because there's no way for them to tell. Also, the problem is at its worst only when in a docked configuration, which may not be common.
5. The reason complaints are escalating now more than before is that this is the first summer that people have had this system (in the Northern Hemisphere, anyway). I think it's safe to say that ambient temperatures are higher for most E6400/E6500 users now.
6. The problem can be substantially mitigated by pointing an external fan at the system.
7. The problem can also be mitigated by software, such as RMClock, that can override the throttling mechanisms in question, at the expense of negating all passive thermal management (though critical temperature shutdown mechanisms may remain in place).