PlayStation now is a game subscription service - basically you pay a monthly fee to be able to play certain titles for as long as you like, or in some cases for a certain rental period. The titles are offered via the cloud, which means you don't even have to download the files to start playing - they're streamed straight to your machine like Netflix. It's a great idea in theory and while the response has been mixed it's not something which is going to go away any time soon.
Sony has just added a bunch of new games to the service from 2K Games, including the first two entries in the Borderlands series and Bioshock, Bioshock 2 and Bioshock Infinite. That's a pretty great selection of high quality first person shooting titles, sure to keep players entertained for hundreds of hours.
There is a catch though - these titles have only been annouced for the US store right now, and the catalogue doesn't always translate worldwide. The other pretty significant issue is that while PlayStation Now currently operates in the UK, it's yet to be offered in Ireland. That's a shame but as many users still aren't particularly happy with the service, maybe it's better to wait until all the bugs have been ironed out, and those prices come down a little.