What are the consequences of being claimed as a dependent (for the dependent that is) in the US?
You are not allowed to have any of your own dependents if you are a dependent (or can possibly be claimed, even if not claimed) on someone's return.
You cannot claim any dependents if you (or your spouse, if filing jointly) could be claimed as a dependent by another taxpayer. [Pub17]
If you are considered to be a qualifying child of another tax payer, you are not allowed to claim the Earned Income credit.
If you are a qualifying child of another taxpayer, you cannot claim the EIC. This is true even if the person for whom you are a qualifying child does not claim the EIC or meet all of the rules to claim the EIC. Put “No” beside line 64a (Form 1040) or line 38a (Form 1040A). [Pub 17].
In addition, the standard deduction that can be claimed is less than that for a single taxpayer that is not a dependent.
The standard deduction for an individual who can be claimed as a dependent on another person's tax return is generally limited to the greater of:
The individual's earned income for the year plus $350 (but not more than the regular standard deduction amount, generally $6,100).
However, if the individual is 65 or older or blind, the standard deduction may be higher. [Pub17]