Disadvantages have been a staple of RPGs for a bunch of years now. They are used to add a little extra history to the character. They are used to give something for the character to overcome; after all, adversity is the stuff of which heroes are made of. They are also used to min/max a character to make him more powerful in one aspect; often to the chagrin of the DM.
Thus far 4E D&D has not incorporated Disadvantages into their game system. However, it would be easy to do so. 4E already has a system of Advantages (the opposite of Disadvantages) and these are Feats. Feats are used to add a slight and unique advantage to a character. I am making a broad and general statement, but Feats are about on par with Advantages in other systems. They are not character or class defining, and the power gained, while something more than simple flavor, are not disruptive to the balance of the game.
Disadvantages are normally chosen at character generation. Taking a Disadvantage allows the character to take another Heroic Feat. I would recommend only allowing 1 Disadvantage for each character. Individual GMs can play with allowing more if that is to their liking.
Here are a few ideas, but doubtless there are a lot more.
Bad Luck: Bad luck follows the character around. A 1 or 2 on a die roll is an automatic failure.
Dependent: The character has someone that relies upon them. This could be a relative (child/sibling/parent), loved one or anyone that the character has a responsibility toward. This dependant person does not have to require a significant amount of time on the character’s part (after all the character is an adventurer and not a baby-sitter), but if the dependant is ever in danger the character should respond. Once the dependant is in danger, if the character is not actively working toward resolving the danger, he suffers a -2 to all his die rolls.
Easily Winded: You suffer from shortness of breath. You need 15 minutes for a complete Short Rest instead of 5 minutes.
Enemy: The character has gained a recurring enemy. This enemy is actively trying to harm the character. At certain points (as deemed appropriate by the GM) the character will be attacked by the enemy or his henchmen.
Frail: You are not as tough as others. Lose 2 from your Healing Surge value.
Hard Knocks: The character has a hard time catching a break. He requires 1 more milestone before receiving an Action Point.
Illiterate: The character can never read or write any languages.
Inept: The character is really bad at something he should be good at. The character suffers -5 to one of the skills available to him from his class choices.
Poverty: The character is incapable of keeping money on him. This could be from a gambling habit, a large debt he is paying off or the need to send his money to support someone else. After money has been divided amongst the party, the character loses half of his share.
Slow: This could be from a birth defect or an old injury, but the character loses 1 from his Speed.
Slow Learner: You’ve practiced it and practiced it but it’s still really hard for you to do. Choose an Encounter power and it is now considered a Daily ability. You can change which Encounter power is affected when you gain a level and choose to relearn.
Susceptible: You have an Achilles heel, a weakness enemies could exploit if they knew about it. Choose one of the following conditions: Blinded, Dazed, Unconscious, Slowed, or Restrained. You suffer a -5 penalty when attempting a save vs. the chosen condition.
Unskilled: The character is just bad at something. The character suffers a -10 to one selected skill. The reasons behind this could be widely varied depending on the skill selected; for example, a penalty in Diplomacy could be from something like bad breath.
Weakness: The character suffers a -2 to Fortitude, Willpower or Reflex Defense. The cause of this penalty is dependent on the Defense chosen. A loss of Fortitude could be from a physical ailment, such as asthma; Willpower could be a brain injury; Reflex could be from an old injury or just simple clumsiness.