This is the jade plant or Crassula ovata. The one in the picture you have has been grown in low light and has stretched out and dropped the older leaves which is why it looks so thin.
The leaves are plump and there are some yellow leaves so it does look to have been slightly over watered.
The wikipedia entry noted above agrees with my experience with them
they require a normal watering when the soil is dry in the summer, and
very little watering in the winter. Overwatering will cause them to
lose their leaves (it is easy to identify overwatering by the
characteristic crinkling look that the fallen leaves have) and
eventually the stem will rot away. Though jades can survive
overwatering, it is best to keep them on a 10 - 20 day cycle in the
summer, and even less (up to a month dry) in the winter. Letting the
soil dry between waterings is essential for a healthy jade.1
They will grow in full sun to light shade. However, they do not
tolerate extreme heat or overexposure to direct sun very well, showing
damage ranging from scorched leaves to loss of foliage and rotting
stems. Most of the common species will tolerate a limited degree of
frost but overexposure to cold weather will kill them.
The intense summer sun where you live can scorch a jade plant so do not put this plant in full sun. It appears to need more light so an unobstructed eastern or north facing window should be just fine.
I recommend cutting it back to encourage new growth and give it a bushier look but that is just personal preference.
Cuttings can be rooted in the same pot or can start a new plant by letting the cut end dry or callous. Place it in bright light for a few days and then push into the soil.
