Gamasutra has posted a nice long feature about what exactly that means, for both companies and for the rest of the industry. As we predicted, there probably won't be huge repercussions for either of the biggest companies involved -- both Activision and Blizzard will continue to go their own separate ways for now, sharing only a name among investors (Gamasutra even says the names on the game boxes won't change at all). The biggest impact will be on the little guys in between -- Activision's previous shareholders now have to answer to Vivendi (who will hold a majority stock in the company), and Viviendi's smaller division, the former glory of Sierra Games, will have to answer to Activision before publishing any of their titles.
And of course the other big consequence we've seen so far is that Bobby Kotick apparently feels he knows everything there is to know about the MMO game. Sure. For now, though, it's business as usual for both Activision and Blizzard -- if there will be any change in either company because of the merger, we likely won't see it for a while.