I've been playing Diablo 3 only a couple days now but have had a pretty frustrating experience so far as well. All the things they listed as benefits for their "Online-Only" single player game are unraveling before their, and gamer's eyes.
Single player games getting hacked? I thought it odd that I had a random person listed in my social list last night, but really thought nothing of it at the time.. guess I will need to investigate that further..
Also, the effin game can't be bothered to save my options! I assume its some issue with it syncing my options with battle.net servers, but what this has caused, is for me to need to completely re-bind my keys every time I fire the game up. 48 hours I've had a ticket in regarding the problem (which apparently is pretty wide-spread) and no response. At first it could take up to 10 mins to get everything set properly, now i have it streamlined to about 2 minutes, but either way, its annoying as hell! (I use a custom keypad for gaming with a non-standard layout that requires almost everything to be rebound, usually a one-time deal and done, but I've re-set everything 10+times in Diablo 3 now)
This *WOULD NOT BE HAPPENING WITHOUT THE ONLINE REQUIREMENT*. Games used to be content saving the settings you've changed in a small file on your computer, now each setting change must be sync'd with a effing server and it's not working Blizzard. If Blizzard can't be bothered to get this working after how many months/years of beta testing, I'm going to turn to hackers for a solution to make this game work properly.