It completely skipped me that there would be a community thread before, since I'm on my first playthrough. Spent last night drinking vodka and exploring past the second bonfire in Anor Londo. Found the giant blacksmith, unlocked the shortcut back to the first area, and then took on O+S for the first time before getting promptly demolished (at level 53, I think). decided to grind a bit to level myself to raise endurance so I could fully wear the Black Iron set (got to level 60 doing this) and then more to raise my Black Knight Sword from base to +5. Started going after O+S later in the evening. It took 15-20 tries while I learned their styles and techniques, and a few times Ornstein and I died at the same time or Smough's electric ass pound caught me off guard, but holy shit it felt good when I finally took them down, and without summoning help. I typically tried to recover my souls, so I ended up with a bonus 30k souls at the end from the runs to the boss.
I think I'm going to return to Sen's to hunt down some of the loot that I missed, plus I need to invade Lautrec. The dark eye notice came up the first time I approached O+S's fog door, but do I have to use the item there or can I do it safely from a bonfire now? If/when I die in it, do I respawn in my world in in his and have to find another dark eye to try again?