Simple question.  How many units lifetime does Vita have to sell before you'd call it successful?

I'll go with 40m.  Half of what PSP did would be pretty darn good with a shrinking handheld market and the 3ds' current stranglehold on third party support in Japan (where handhelds sell best)

40 million but with an attach ratio of over 6 games. I consider the PSP a failure, it might have sold quite a bit, but it didn't move software.

why do people always abbreviate it GCN?  You are referring to the Gamecube right?

When more 3rd party developers take notice to it and start the oven and cook up some great games that will appeal to alot of diffrent people, Selling more vita's not just to the "core" but everyone. The 3ds sells so much cause it has so many diffrent games for everyone to pick up and play not to mention its more affordible which is a bonus. But i would consider the Vita a success if it can sell atleast 25 mil + atleast beating the gamecube worldwide sales, anything less then.. yeah.. a great peice of hardware that will be forggotten.

I hope for the best of the vita, I had a PSP yeaaaars ago and it was pretty cool. Now i am looking for a new handheld and hands down it will be the 3ds has more to offer.

Six games per console on a handheld just isn't going to happen.  Digital distribution is just too much of a factor and it's only going to go more in that direction with every passing year, especially with PS+ factored in.  Attach rates for all systems going forward are going to have to be tempered with that in mind.

It would have to sell at the very least as good as the PSP did, which honestly I don't see happening.

Digital distribution still counts as games purchased. I probably wouldn't count free games from PSN+  

i think Sony isn't marketing Vita right.

100M.

You beat me to it! But yes, that is how Nintendo wanted it.  True story.