There is a rumor going around online that you will be able to play PS1 and PS2 games in your PS4 through software emulation that will be available for download. This is different from the PS Now streaming service they are going live with in a couple of months. Awwww shizzle.
Edit: This was in a recent Digital Foundry report. Apparently the Playstation Now service will only be for PS3 titles. This HD emulation will handle the PS1 and PS2 catalog.