Not very good from current information rumblings and market trends.
When PS2 launched, its sales were fed in huge force by three main things. New games, backwards comptability, and DVD playback.
Now, from current estimenets from developers...It takes 3 times the $$$ to create a title on the PS2 than does the Xbox. Why company choose the PS2 though is that they make that moey up since the install base is so large. The operating system which run the PS2 is said to be developed by the same people whom created the first one. Now if this is true and developemnt costs are still high and complicated...You can see that companies may choose other consoles from the get go.
In reguard to the DVD playback. The PS2 got approve purchase from parrent becuase of DVD playback. DVD was the new wave of Video and people wanted to have means to play it. The PS2 answered this along with game. With a lack of a new medium...The PS3 will not sell as quickly at start.
In reguards to Backward compatablitly: There will be a limitation to how far they can emulate other console lines within the same company before it become not very cost effective and bogs down on the system. IF backwards compatability is offered for the PS3, the price of the console with be sucked into making it that way, as well as the added note that the Sony console line will use the same controller for over 10 years.
In reguards to the Games : The PS2 huge preliminary sales were due to hype. The Games the PS2 offered in it first line up were So-So and lacking graphicly, so one must assume people first bought becuase of the DVD and PSOne features, in addition to later knowing there would be games. Without a strong first line up, the PS3 could and wil be in some hot water if new consoles from MS and Nintendo are launched with strong games.
With the other console started sales before teh time of Sony, they stand a chance to take developers away from Sony if they see that one console appeals to them more that the current PS3 build.
An interesting note about Xbox. M$ uses Direct X technoloyg in the Xbox which is fimilar with developer becuase it has been arond a while on PC. With the Xbox's fimilar development kits vs Nintendo and Sony proporitey systems....Will some developers go to the gree side to save themselves money in leaning the new software?