I remember a great TV commercial.
It showed a guy in a nice convertible car on a sunny day, with a big box in the back seat that said on the side “New State-Of-The-Art TX5 Computer!”, and the guy was clearly driving home from the PC store with a satisfied smile…
… until he spots workman who have just finished putting up a billboard next to the road which says:
Buy the Brand New TX6 Computer!
( and the punchline was that you should lease your PC from such-and-such company that would replace your PC periodically. )
The moral was that there is always a faster and more advanced device a month or two down the road.
PS The only clear cut major model change in the future would be the first drives that also allow writing to a DL DVD-R disk, but that won’t be until 2005 because there isn’t even an agreed spec yet.