Q:

What are the advantages and disadvantages of being ambidextrous?

Most of us have one dominant hand. We find it nigh on impossible to do very delicate or dextrous activities with our other-hand. This seems like an apparent weakness, and a rather odd one when you first think about it. 
Cursory internet searches revealed unexpected findings. One website said it has mostly negative effects on the brain. However I don't trust the source at all.
I'd be interested to know about the "story" about the good and bad of ambidextrous physiology. Particularly, I am interested in the neuroscience of ambidextrous people. 

A:

I think that the advantages of using both hands with equal ease is quite evident whether it be sports, at your work or while you are doing your household chores. 

An obvious advantage is using both hands to write or draw with both at the same time.
I would be focusing on the disadvantages that may be faced.

1) Ambidextrous people are more prone to suffer from Synaesthesia
  (reference)
2) They are likely to possess (not necessarily) the LRRTM1 gene which
  is linked with Schizophrenia (reference). 
3) They score lesser in intelligence testing (reference).
4) Mixed handed children are more likely to suffer from ADHD
  (reference).
5) Mixed handedness is associated with greater age-related decline
  (reference)
6) They are easier to anger and influence emotionally (reference).

There are quite a few studies that have pointed out that it may not be all that good a condition but Leonardo da Vinci who was probably the most diversely talented man who ever lived is said to have been ambidextrous. He apparently could draw with one hand and write with the other at the same time, so I would have to say that the positives of the condition are extremely good (reference).  
edit:
This probably qualifies as a second question :-D but I just saw a thought by biogirl in the comments section on "whether our ancestors used both the hands and using just one hand is recently evolved" and she has a point there. From a study publlished in 1977 I quote. 

The predominance of the right hand over the left was also reported
  among Egyptian art forms 3,500 to 4,500 years old, where the ratio of
  left- to right-handers was 9:111 and 5:100, respectively. However,
  going further back using the "Draw-a-Man Test," found that ancient
  paleolithic man, from 1,750,000 to 8,000 years B.C., was probably
  either more ambidextrous or that there was a greater proportion of
  left-handers than there are now. (reference)

Also from a study titled "Evolutionary Back Grounds of Human Left Handedness", the authors concluded that 

For most manual tasks, especially those tasks involved in competitive
  activities, increasing performance by the specialization of one hand
  is certainly adaptive. Aggressive interactions are responsible for
  fundamental selection pressures acting during primate and human
  evolution. The higher prevalence of right-handedness might well be due
  to a previously existing cerebral bias. But the specialization of one
  forelimb leading to right or left-handedness is better viewed as the
  result of natural selection. (reference)

