[joosters]

That's definitely another factor. Again though, I doubt it's the limiting one. No-one (as far as I know) has produced a power-hungry CPU with (say) 5000 registers on it.

[terrymah]

I've heard that modern Intel processors have 100 < x < 200 physical registers. I'm not sure they actually document the exact number.

[hornetblack]

Itanium has at least 256. (128 Integer + 128 Float + 128 predicate (1 bit), which are essentially flip-flops.)