So, there's been rumors aplenty about "Yahoo!'s new Sikkret Social Site" thingy.
Let those rumors be laid to rest, presenting mash.yahoo.com.
Of course, the best description of what mash is would be on the official mash blog. In a nutshell, it's a place where you can play. Where things get interesting is that other folks can play with your page too.
Think part myspace, part wiki, part... well... whatever you want to make it, or your friends make it. Or if you're a particularly trusting soul, whatever you want random strangers to make it. (Best thing is that you have to approve those changes so it's not like you're going to become an unwitting shill for Canadian discount aspirin gambling rings.) Plus, there's a way to revert everything or roll back changes if you, your friend, or random evil person screws things up.
Mash gives you a lot of flexibility to do a bunch of stuff. Applying styling info is pretty straightforward (d'oh, don't include the trailing '/'), as is adding new modules for stuff like videos from YouTube or photo streams from flickr or flash objects (no javascript yet), although there are hints that module development is not far away.
What about 360? Well, everything I've heard is that it's not going anywhere anytime soon. It's my understanding that while 360 is nice, this was the product of one of the first Yahoo! Hack Days and showed how to make profile pages even better. Plus, 360 and Mash are really products for two different audiences, so it makes sense to keep them around. Still, I'm not part of that team nor can I really say what the long term plan is for these. For now, Mash is the toy (honestly, it's as much a toy for us as it is for you. There's some pretty cool tech that we're working on related to this so even if you don't think it's particularly noteworthy, you may want to keep an eye on their blog.)
So, how do you get a page? Well, it's in open beta right now, so you quite literally "have to know someone". The way it works is that "someone" has to create a basic profile page for you and the system sends you an email. You get the email "claim your page" and go to town adding stuff (so yeah, expect some idiot to be selling "invites" on ebay later this week).
Pretty cool.