Patches :
Well, Blizzard doesn't give up that easily and create another new patch version 1.04, This we all ready. In just three hours after the released a couple of cheating programs already on the Net. I guess hackers is a little bit faster than Blizzard programmer!!!

Seed Option :
Seeds were an option that was available in the demo, where you pressed "r", and got a number that represented the 'blueprint' to which the dungeon was generated. There was a program that allowed you to enter in your own seeds to try out other people's dungeon blueprints or repeat one of the ones that you liked before. You can't do any of this in the full version, probably since it could take away from the randomness of the game.

The Level Random Generation Engine :
There seems to be a database of levels containing a list of all the monsters, level layout, treasure and other stuff to be found on the level and treasure to be found on the monsters for that level. The random generator selects one of the "blueprints" to create the level. For the single player game, I noticed that if you reload your game and kill the same particular monster over and over, you will always find the same item off its body.

Monster Hit Points :
Monster with 100 hit points (HP) in single player
In multiplayer Normal mode the HP increase 2x monster with a single player (200 HP)
In multiplayer Nightmare mode the HP increase 3x monster with a normal mode (600 HP)
In multiplayer Hell mode the HP increase 4x monster with a normal mode (800 HP)

Monster Immune System :
Some monsters in hell on hell difficulty are listed as being immune to fire, lightning, and magic, but that isn't exactly true. Blizzard has noted that there are no monsters that are completely immune to all forms of spellcasting. Those monsters which are listed as being immune to everything can actually be affected by Stone Curse and Apocalypse and perhaps other spells too, however the Devil himself (DIABLO) are the only one that immune to all the spells.

Experience From The Monster :
Each monster is worth a certain base experiences (XP) amount and then has a negative XP modifier for each of your characters level. For example (you can find some monster XP stats in our monster section), a Blood Claw has a base of 5425 and a modifier of 187. If you were 20th level when you killed the Blood Claw, you'd get [5425 -(187*20)] XP or 1785 XP. When you reach a certain level (In the case of the Blood Claw ~level 29) You will receive no XP because of the cumulative effects of the negative modifiers. You can't receive below zero XP for any monster however, no matter what level you are.

Monster Do Regenerate :
Yup, monsters regain hit points, although the tougher monsters tend to regain them faster than weaker ones. You should try to kill a monster once you've hit it instead of switching monsters to attack before you've killed one of them.

Magical Items Generate As Follow :
When you find a magical item, it will have either one or two magical item adjectives. There are two main types of adjectives. One type is only found before the base item in the description (ie. "Weird" in Weird Axe) and the other type is only found after the base item (ie. "Zodiac" in Ring of the Zodiac). Sometimes these adjectives are combined as in Weird Axe of the Zodiac. A list of all the before and after adjectives can be accessed from our Adjectives section.

Quest For Multiplayers :
The only multiplayer quests are the Butcher, King Leoric (Skeleton King), Archbishop Lazarus, and Diablo.

Dots Recieve During The Battle.net Channels :
The dots represent the "soulstones" that you get from Diablo slayings. The first dot means that you've killed Diablo on normal mode, the second means that you've killed Diablo on Nightmare mode (you also get the first dot for doing this if you don't already have it) and the third means that you've killed Diablo on Hell mode (you also get any previous dots you don't have) When you get the maximum of three dots, then your character's box gets outlined in gold as well.

Using ID On Battle.net :
To get the battlenet ID, type /whois {charname} without the braces while on a Battle.net channel. It will return a unique number for you or whoever's name you have entered. You don't get a unique ID for every char you have, so if you have two characters on the same machine, they will have the same ID. This can be used for several purposes. One theory is that people with extremely high ID numbers (ie 200000+) or so and characters that are like 45th level, it might mean that they have cheated to get their character that high since they wouldn't have been on Battle.net that long. This is by no means a surefire way of determining cheating however. They could have built up their characters outside of Battle.net before joining or have been rapidly playing Battle.net 24 hrs/day for the last week or so. Another use of the ID is to tell who a person really is. With all the character editors and multiple characters floating around, it's hard to tell who just Townkilled you. However, with their ID in hand, you can know for sure who to get revenge on or put a bounty on.
P.S. /whereis (charname) also works too