Notch noted on his blog that Minecraft version 1.5 went live today and it's time to update your servers.
The addition of weather effects such as rain, snow and thunder have made it into the live version of Minecraft. Markus Perrson, Notch if you're nasty, first announced the next update would feature weather on April 7th, and it took the Mojang team less than 2 full weeks to implement it into the code. If that's not a quick turnaround, I don't know what is. Also in this update to version 1.5 is statistics and achievement tracking as well as two new kinds of rails for your minecart: detectors and powered rails. Notch is far from done, as he's further tweaked the performance of the game and will continue to develop more statistics code.
"More statistics and achievements will be added over time as we develop the game," Notch said. "They're only stored locally at the moment, but we'll slowly be rolling out online storing of achievements over time."
While I'm sure that stats and achievements are a welcome inclusion, and the cosmetic addition of weather will increase immersion, the real gem of this update is the update to the rail system. The Detector Rail - made from iron, some redstone dust, and a stone pressure plate instead of sticks - will allow players to create train systems. The Powered Rail, made with gold instead of iron, replaces the various methods used to "boost" carts which players resorted to.
I can't wait to see the rail systems that players can make with the new rails available.