In my opinion i think 5 or 6 years is Plenty long enough. I would also personally be happy with them lasting as little as 4 years.

How long do you think is appropriate?

8 years. I'd like to think that I paid $649.98 so my hardware would be relevant longer than when I played $349.98 last generation.

5 years.

Next Gen I want upgradable consoles, similar to PC, so consumers decide when they jump into the next gen by assembling new updated components.

Also, 6 years seems good enough to me. You gotta maximize the money you spent.
for my case just make the maths, bought all this new BRAND NEW:

DS Phat at launch + PSP (not at launch but bought at launch price) + Wii + 360 arcade (for 130 bucks)

Oh gawd, counting the games in, plus Live subscription, and Wii acessories I could already marry and buy a car.

as long as it takes for PS3 to outsell 360  

A generation should be over when the Tech has been Maxed out and/or when a new relevent Tech can offer something new/different/ VASTLY improved. I'm still a wii only owner beacuse i refuse to spend 2 car payments to play re skined games from last gen. keep in my that this is only my opinion, and not to be taken as fact for everybody.

I hope the actual generation last 8 years, with the 8th year being the year where the next gen are announced and shortly released.

Long console generation FTW!!!

short console generation FTL!!!

5-6 years

As long as improvements are being made to games and there is something to look forward to. For instance, right now we have games like MAG, GT5, FFXIII, XIV and Mod Nation Racers that are each supposed to bring something new to the table.

I still think all three consoles this gen. have at least another 3 years in them.

About 7-8 years, The PS2 was 7 years old when the PS3 launched correct? That would be perfect length in my eyes