Though the shutoff date for the North American Demon's Souls servers has been pushed back thanks to continued support from fans, the end is near. According to Game Informer, we've got until May 31, 2012 before the servers are turned off by Atlus, which should be plenty of time for those players who have yet to jump in.
Good timing, too -- the PC version of Dark Souls was just confirmed today. If you feel like you're going to play this spiritual successor later in the year, it's worth seeking out a copy of Demon's Souls while the oft-praised multiplayer is still functional.
Leading up to the final days, Atlus will put on two World Tendency events. The first event will run from May 1 - 15, followed by the second from May 16 - 31. It's been a good run.
Demon's Souls Going Offline End Of May [Game Informer -- Thanks, SephirothX]