Sony had initially said that the PS3 would be around for ten years before the PS4 was released. However, since Microsoft have announced the advent of the XBox720 Sony have mentioned that the PS4 maybe out around 2012.
This year will see the release of the PSP2 and possibly the release of the 3D modification for the PS3 (funny looking 3D glasses will be required).
The PS4 is reported to be using the new HVD (Holographic Versatile Disc) which again will hold about five times more information than a BluRay Disc. Using three lasers a HVD device will read information off the disc's hologram in three-dimensions and not just two. This extra capacity will be required especially for all the 3D media that's about to wash over us all.
HVD will probably be the last of the disc type media formats as solid state memory takes over. You can already buy memory-sticks that hold more data than BluRay discs. The PS5 will cease to use discs and will rely on solid state memory devices and downloads. This will make the machine a lot smaller than the PS4 and with the addition of its own on-board screen the PS5 will also replace the PSP2/3.