The intent of this list is not to make Blizzard look bad; in fact, compared to most other computer games out there, Diablo is exceptionally stable and bugless. The intent of this list is to educate and provide insight for anyone wanting to see what parts of the game don't work as intended or are strange. This list was constructed on the Diablo Strategy Forum, from the people who know more about the game than Blizzard itself does. :)
Heartfelt thanks and a major thumbs up to all who've contributed bugs or helped explain them so far: Agammaglobulin, Argus McFrugal, Armin, Bolty, Charles Warren, Claudio(Cat), Code Myster, Cyrene, Darkman(BNM), Dark_Slayer, Das Regard, DaveMcW, Dr. Disaster, Dr. Zed, Drasca, El_Gecko, Erthshade, Esau, EviL, felisandria, Flux, Frank, Frenzy, Gorakh, Gyrefalcon, JakRabbit, Jarulf, KingOfPain, Kipo, Lance, Lochnar, M., Mayaheine, mellymel, moe SAINT EverGreen, Mystifier[CB], NoVit4Me, Nystul, Omega, Rand'al, Rich, Ruger, Tahrajj, Thecla, the Sage, Saxywoo, Sourceror, StormDemon, Stu, Tommi Helminen, Uwain, Van Damned, Varaya, and Walkiry.
Unless stated so, all bugs are multiplayer bugs. Some may apply to single player mode, some may not. Also, a key point here: many of these bugs aren't really bugs, but strange behavior, or quirk, in the game that was probably intentional. The reason they are in this list is because the list is meant to be an educational tool to point out quirks of the game to people who've never heard of them. "Quirk" bugs are indicated with this color text.
To date, two immediate game-crashing bugs have been identified in version 1.09. They are listed in this color text.