Let's say you have a top of the line computer. What "normal" activities that happen on the computer can slow the machine down? By "normal" I simply mean nothing too out of the ordinary. Something out of the ordinary would be running an infinite loop that consumes 100% of your processor.
For me, the thing that slows down my computer--and I would imagine even top of the line computers would suffer the same syndrome--quite a bit, is when it's downloading 10 files simultaneously at the total speed of 0.5 MB per second. All the background applications take a toll.
Another thing is ripping or burning a DVD.
Another thing would be video editing (writing to file).
How about you?