>>Wouldn't you really just need to have two accounts
Yeah, that's one way to go. But it's a hassle to be signed into two at once. Not a huge hassle, but using two browsers at once is just beyond the average dipshit user.
Companies need to tread very carefully when they make big changes. One thing I used to enjoy about Yahoo previously was the aliases. You signed into your account with one main ID, but you could have sub accounts that looked to others just like a separate account. So it was easy to be "JohnRSmith" to one group and "hung4fun" to another. They did away with that, and the outcry resulted page after page of angry comments on the developer's blog.
And then to add insult to insult, they made a second huge error at the same time, in a belated effort to be more facebookey. They blanked out everyone's profile, in an effort to force them to migrate to the new facebook-ish profiles. And now a year later, the vast majority of Yahoo users have blank profiles. They simply didn't use Yahoo in the same way they used Facebook, and they didn't want to.
I think it all came about as a result of Yahoo realizing that their core constituents were aging, and that the kids had moved on to something new. The right way to respond to that was to buy MySpace in about 2001, but Yahoo is too slow and dumb to do things like that. I was working at Yahoo in 2001 when a co-worker said "dude, you gotta check out this MySpace thingy. It's full of hot young babes and it's free". Within a month, all the Yahoo employees had a MySpace account. When all of your employees are using some other website, that's maybe a clue that you need to take action. But companies get big, then they get slow, and then they get dumb. Then they (usually) die. It's the circle of life, I suppose.