Wow! I mean WOW. It’s been 40 years since we’ve seen a type Ia supernova this close and we’ve never seen one as young as this. Not that this just happened, it actually happened 25 million years ago, but we are seeing it almost at the beginning, just a day after it started. It’s in the spiral galaxy M101 and it may get bright enough to see with binoculars in the days ahead.
I know I often link to the Bad Astronomy site, but that’s because Phil Plait has the best astronomy site out there IMHO. Check it out, you won’t be sorry. http://blogs.discovermagazine.com/badastronomy/
There’s also an article at the Universe Today site with some more technical info: http://www.universetoday.com/88447/shiny-and-new-supernova-spotted-in-nearby-galaxy/
Edited to add: The official name is now SN2011FE. It has been brightening as expected and is visible through home telescopes. This site has the best directions for finding it that I’ve seen: http://astrobob.areavoices.com/2011/08/27/how-to-find-the-new-supernova-in-the-pinwheel-galaxy/