Wait til you get halfway or so through A2 Inferno. The difficulty ramps up hugely.
A1 Inferno I can solo, but again, if any elite in my way has a tag like Mortar, it's an instant restart for me. I can't stand within the mortar range, because the elite steps forward and kills me, and I refuse to spend 10 minutes kiting while my hydra kills them. There simply is no other way around this for a wizard...
The Lacuna Huntress in A2; I can Fraps a video of them one-shotting me with Diamond Skin on if you really don't belive it. Over 35k damage instantly from them jumping out of the sand. My Templar merc with 60k life dies in under 5 seconds vs elite packs here also.
The multiplayer is impossible I think because it's so new... I see tons of players with 298 dps weapons in Inferno games; which means they do not contribute to killing (not enough to notice anyway). My friends are all happy in nightmare with their second characters, so if you had a friend that works hard, then yes, Inferno is possible... but don't ever expect anything from a pub game.