On the other hand, the problem's been that Yahoo wasn't actually the best anything. Casual web? AOL. Search? Anyone else, then Google. Email? Copied Hotmail, then GMail came along and they never really caught up. They purchased a bunch of top-notch companies and then let them stall into obscurity.
So, perhaps the comparison isn't going to hold up. Still, these companies should be warned.
Social can drive group activity (my wife planned her HS class reunion mainly through FB), especially group sales.
This could be Facebook's big "monetizing" event that breaks them out of the hype area and squarely into heavy profits.
No one is in a better position than Facebook to facilitate group buying. The synergy-meter has burst into flames.