Why I say its more of a hack rather than a tweak is because - hyperthreading is not true SMT, is very application dependant (and can be detrimental) instead of being a general optimization, is specific to the P4, cannot be reused and is not implemented in new Intel cores like the Conroe.

If Intel meant HT to be such a good 'feature' HT would have been incorporated in the very first version of the P4. The first P4's had totally absmyal peformance, took several iterations to be HT capable only to be somewhat approximately on-par with single core A64s and finally the HT 'feature' is conspicuously absent from the Yonah and future Conroe/Merom.
Well to be honest, thats just a matter of differing opinion. When a design's weakness is somewhat fixed by additional technology, I am happy enough to call it a feature not a hack.

The reason that Intel didnt put HT into their next gen cores? Who knows? It probably has something to do with the fact that physical multicore chips are becoming the norm now, and thus far outstrip the performance of a single core with an aditional logical processor. Surely though we will see more advanced SMT features in the future, probably when the new gen matures a little and the limitations become apparent.