and think og how long VHS stuck around. i work at a blockbuster and we JUST destroyed the last of our VHS inventory about 3 weeks ago. and people still come in complaining because we no longer carry vhs!
my prediction: DVD will remain the standard for at least the next 5-6 years and won't be totally phased out for another 10 or so.
something interesting to think about though: online rental services are already making HD titles available for rent. These services are quite affordable and may facilitate HD's infiltration to the mainstream so it's possible my timeline might be shortened due to this.
the main limiting factor, in my opinion though, will be the pricing of the hardware.