There are many lessons we have learned, but if you ask me to pick one lesson
Before the launch, as far as the hardware goes we didnt put enough resources in the hardware to allow us to develop games that are unique to the PSP compared to home consoles. We had many products on PSP, but most of these games like God of War [Chains of Olympus and Ghost of Sparda] came from the console. Basically, you can play a bigger, better version of these titles on PS3. So pre-launch of PSP we were too happy with having the basic capability of PS2-class games to play on PSP, in terms of the screen and CPU/GPU. But after the launch and a few years time, just having pretty graphics isnt enough. Especially when you can play a bigger, better game on home consoles. Thats the one big lesson when we designed the PS Vita. Because it is portable and because its a new technological development, we can put a touchscreen, touchpad, cameras, GPS, or 3G capabilities. We made sure that developers will be able to make use of these features that are unique to portable systems, so that with games we can continue to produce something very exciting that you cannot find on games on home console. So thats one lesson.