Does this make sense?

[Undertoad]

You already knew at gut-level, there's no sense in using Moore's Law (18 months) to decide what computer you want.

(And it doesn't apply to RAM or hard drives at all.)

First determine what it is you want to do, or are likely to need to do with this system. You'll have it 3 years so figure out what you'll need to do in 2.5 years with it.

The numbers following each item are importance from 1 to 10 of CPU, size of hard drive, quality of video card, size of RAM.

Hardcore gaming 8 - 9 - 10 - 9
Creating complicated content (movies, large images, music etc) 9 - 10 - 7 - 9
Pirating complicated content 8 - 10 - 3 - 3
TV & cable replacement 5 - 7 - 5 - 5
Creating simple content (docs & spreadsheets) 5 - 5 - 3 - 4
Browsing the whole Internets and doing everything you can do there 5 - 6 - 2 - 4
Casual gaming 4 - 1 - 2 - 3
Browsing the Cellar 1 - 1 - 1 - 1

So IF you are planning to play the latest and greatest shoot-em-up game in three years, invest in some beefy hardware and 8GB. But IF you are just browsing around, you don't need something complicated.