Besides the gift tax mentioned by the previous replies, another tax consequence is that you "inherit" your parents' cost basis for the gifted property, likely increasing any capital gains received upon selling that property. You do not receive a stepped up basis like you do when you inherit the property.
Although not tax related, you and your parents need to remember that if you are a joint owner of any property, that property may be liened or seized to pay any judgments against you (e.g., credit problems, personal injury lawsuits, etc.). Your parents should be warned of the risks before proceeding.