InWorldz, an OpenSim-based virtual world, is garnering a fair amount of attention from Second Life users, especially those chafing at Linden Lab's exorbitant land fees. And while it definitely has a lot of potential, NWN alumnus Chestnut Rau isn't sure it's ready for prime time:
Nothing rezzes even when I wait a long time. I find it impossible to TP without hanging up or crashing. Textures, when they load at all, flicker in an epileptic fit inducing manner. I can barely walk without rubber banding or getting stuck totally. Seriously? SL in 2007 worked better for me.
Much more here. I haven't tried InWorldz yet myself, but I trust Ms. Rau's perspective implicitly. To be sure, InWorldz may have advantages over Second Life, growing pains aside.