Diablo 3 will be by far one of the worlds most botted games. In diablo 2 you could create bots that would run dungeons for you with ease. Diablo 3 apparently will have dungeons that are constantly changing so a teleportation bot wont be able to instantly find the end of the dungeon. However this does not mean the game wont be botted.
A bot in diablo 3 will do all the things you can need. From using the correct spells based on mobs, to healing you when needed, to collecting only the best items you are after in the game. Also bots will be nearly undetectable because of the root kits now available to all programmers when it come sot making great hacks.
You still need to remember that blizzard is very intense when it comes to botting in their games. They will not allow anyone to use a bot and not be banned. So if you do decide to bot be forewarned there is a chance you may be banned. However on the better side you wont have to worry about a player reporting you because you hopefully make private games again that will keep your account safe.
For premium diablo 3 be sure to check out the forums.