So simply put, now is your time to try out the game if you want. If you like it, when Notch gets his site running again. But the game. It is currently in Alpha and at 1/2 price. Should be $9.95 Euros I think it was or about $13.50 US.
The following is taken straight from Notch's Tumblr page which can be found here.
Notch wrote:Free Minecraft until this gets fixed
Phew. Wow. I never should’ve tried doing an update without fixing the performance issues.
I’ve disabled everything CPU intensive on the web server now, and put the downloads on an Amazon Cloud thingie. Since I’ve disabled payments as well, this means that Minecraft will be free to play until this all gets sorted.
For more information, go to http://www.minecraft.net/
Also, depending on how things go on Notch's end, this may be slightly free longer than he'd like. So act now on this limited time offer. =D