As someone who has a preference for the 360 over the PS3, allow me to present my opinion:
Yes, the 360 will be outsold by the PS3 by a signifficant margin worldwide in 2008. It will NOT pass it in lifetime sales, but it's sales will likely be a full 50% higher than the 360's in 2008. As you'll see in my sig I expect it to be within 4 million worldwide. There are many reasons for this.
First, consoles tend to peak in their 2nd full year on the market. Not only did the 360 just have that year, but they also released a massive amount of quality titles including what is undeniably the biggest title the system will ever have in that year. Add to that the fact that the 360 ALSO had a price drop, and even created a viable low-end unit with the Arcade (finally) and 2007 was the 360's best year. The chances of the 360 ever doing better than it did in 2007 are very very very very VERY low.
Second, assuming Blu-ray kills HD DVD this year (something very likely at this point) the Playstation 3 will still be a very reasonably priced Blu-ray player. People do tend to overestimate this though for a few reasons. First, once HD DVD is dead Blu-ray players will come out that are much cheaper than the PS3. Second, a lot of people simply buy their movie players by walking into that section of Best Buy, and the PS3 won't be in that section. Still, this will boost sales.
Third, 2008 will be the strongest year in the PS3's life. Just as 2007 was for the Xbox 360, 2008 will be for the Playstation 3. The Playstation 3 has a large library of major exclusive games for 2008. Gran Turismo 5 is their Halo 3. It will be the best selling game ever released on the system. The 360 is depending on new IPs in 2008 (the same thing the PS3 tried to do in 2007), which really doesn't work well for systems very often.
So, in conclusion, the PS3 will gain on the 360 in 2008 significantly. Lifetime I expect them to end about equal (like the GC and Xbox did). Again, I greatly prefer the 360 over the PS3 right now in game library, so I'm not saying this because I love the PS3 and "want it to win" or anything. This is just my logical analysis of the 2008 situation.
