Well I meant it as in "did they even consider single-player balance with the new content or will I just be brutalized, frustrated and not have a good time?" I'll probably pop over to one of the NeoGaf servers at somepoint but right now Terraria is more of a single player time-sink for me.
It doesn't feel balanced any differently from how Terraria has always been balanced imo. The balance in the game has never really felt like "solo" or "multiplayer" to me, but instead the game is entirely balanced around item tiers. If you're using tier 1 equipment against tier 3 enemies, the game will feel really really hard, and beyond that it is simply impossible. As you gear up through the tiers, the game gets progressive easier, even as enemies get harder.
The difference in 1.1 is that now they've finally implemented true "end game" content in the sense that there is a sort of end boss in Hell now for the normal game, and after beating it the entire world changes into a more dynamic and much harder mode with huge amounts of new content. This basically resets the difficulty of the game drastically, regardless of that equipment you had when you beat the boss. Even if you have all the best equipment the game has to offer up until that point, the world changes will still make the game incredibly challenging.
From this point on, you then have to re-explore the world and basically start to discover what has changed and learn the new rules of the world, while seeking out new equipment, new ores, so you can improve your equipment once again with the newly unlocked stuff that's now available.
If you are able to play Terraria solo, you'll be able to play the new stuff solo as well. There's nothing changed that makes it particularly different. It should be noted the multiplayer Terraria very often comprises of a bunch of players on the server in completely different places doing their own thing. Sometimes the players will group together in pairs or in large groups to do something together (fight a boss, build a tunnel, explore a new biome, etc) but it's really more about the social aspect than a balance aspect.
Hope that helps!