On my I7 laptop - I tried, it gets too hot, so bottom line is that TThrottle would slow down so much that at end does not make sense.

If I had to buy a new machine to crunch - no more laptops, sorry.

I have one, targus. Perhaps you could say it is not that efficient that specific model, but I barely notice the difference.

IMHO there is little you can do with the small surface open for heating disposal in a notebook. The bottom is almost completely closed. The space inside is on purpose kept at the minimum. Processors are too powerful for that kind of space and heating disposal solutions. Not done for running 100% for hours.

And if you think, apart from us, who needs to run 100% 24/7 on a laptop?

Crunching with hyperthreading ON is a benefit for a couple of reasons:

1) It significantly increases your computing power for only a marginal increase in power consumption

(consider the i5-2500k and i7-2600k are both 95 watt cpu's even though the 2600k can produce 20-50% more points per day on WCG)

2) Having 2 threads running on one core will increase your WCG "run time" by a factor of 2

Of course if your system is a laptop it may be better to have it off for thermal issues, but in a desktop setting I would always take hyperthreading vs no hyperthreading

I always use HT on desktops. Even with an Intel heatsink (just don't OC).
I don't always use all threads to crunch on though. I often leave one free to improve system responsiveness; I also crunch for a couple of non-intensive projects (freehal and wuprop), and GPU projects (that use a little bit of one thread).
Did you try HT on, Turbo off, and/or reducing the clock speed using power options?