Is hyperthreading really useful for normal day to day computer use?

not really.
Hyperthreading uses unused execution units, if the two programs are unrelated yes hyperthreading will have a huge impact however the light tasks of word processing and surfing is very light and you wouldnt see any difference in performance.
HT needs very heavy cpu oriented tasks to see if it makes a discernable diiffrence.
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I'll probably wrinkle some foreheads with my comment since I've been arguing on other threads that Intel shouldn't be so stingy with hyperthreading, but according to what I've read hyperthreading gives maybe 10% - 20% boost in performance overall.