|Temporarly down because MPAA/RIAA/etc are above the law.|
TPB has released all their code and torrent databases so everyone can create their own versions. I've heard they are creating a decentralized site that could never be shut down.
They shall rise again ! However, it's the longest PirateBay has been down since about 3 years, if I recall correctly. No one knows exactly when it will be back online, but several people are working on it, last I heard.