At the end of the day it doesn't really matter who has the best chip, it's who sells the most and at the best profitability. Leading edge and best of breed has seldom equated to massive sales figures. If it did the majority of us would be looking at this web page on a Mac! (No, I am using a PC with XP!)
What effects the business of Intel and AMD is the performance of the PC companies. If you look at the lineups of both HPQ, who have made good progress in terms of profits, and Dell, who have not done so good, their lineups are pretty much dominated by INTC products. The 64 bit mkt is the exception where AMD is the player.
But you have to rate the PC business as 50:50 right now - 1 big guy is doing well, the other not so well. I suspect Dell's AMD announcement was more to shake up INTC when it comes to negotiating the price for processors, I don't for 1 minute believe either of them will move substantially away from INTC. However if a real price war develops on PC's then margins of both processor companies will get squeezed, and maybe for no growth in sales.