2009/2010 is a pretty safe estimate for the release of the next Sony and Nintendo handhelds being that they will be 5/6 years old; this will give the Nintendo DS another full year of dominance in both hardware and software sales before the next dominant handheld unseats it.
With Home consoles 2010/2011 will be when the first of the 'Next Generation' consoles will be released and by the end of the following year (2011/2012) all of the 'Next Generation' consoles will have been released. The dominant console from this generation (probably the Wii) will continue to remain dominant until all of the next generation systems are released, and will (probably) still sell on some level until 2013/2014; the other consoles are (likely) going to see declining sales after the first 'Next Generation' console is release because they will lose their position as a 'main' alternative to the dominant console.
