Liquid nitrogen or helium. But if someone went to the trouble to use these substances, they'd likely show it in action instead of some computer screen.

Clock speed hasn't increased, but instructions per second per core has more than doubled over the last decade, and instructions per clock cycle per core continues to increase (http://en.wikipedia.org/wiki/Instructions_per_second). Slower than Moore's law, but it's something.

> I know that FSB speeds are irrelevant now more than ever with multithreading and multi-core architectures

Clock speeds have been irrelevant ever since there has been more than one architecture for the same instruction set. You cannot compare a 3GHz i7 with a 3GHz Pentium 4 of equal core count and say that, just because the clock is ticking at the same speed, Intel isn't doing enough to improve performance. There would be a vast effective difference in just about every kind of workload, just due to architecture improvements.

This cap also has to do with physical limitations of signal propagation times and the limitation of memory as we know it today. Even if external memory wasn't the bottleneck annihilating the purpose of a faster clock, internal registers need a certain time to retain electricity. Silicon is only so speedy! More compact architecture (1nm dies would be nice, right?) could allow for quicker propagation times and thus faster clock speeds.

I kind of like that my 3-year-old laptop doesn't seem like an ancient, sluggish piece of junk compared to the current models...

There's a reason for that clock speed stall and it certainly isn't for lack of trying. Billions have been thrown at the problem. It's just a fundamental limit of transistor design and heat dissipation. If it were possible to manufacture 8ghz cpus that could run reliably for years they'd be on the market.