How dangerous is cobalt(II) chloride used in silica gel balls?
Cobalt poisoning is apparently very rare. The only situation in which cobalt poisoning is a serious problem is when it is exposed directly to your bloodstream (Recently it has been an issue with people who have undergone certain hip implants -- see this page).
The amount of Cobalt chloride in silica gel balls would be absolutely harmless. According to most sources, you have to be exposed to significant amounts of cobalt (at least more than 20g for an average adult) for a long period of time for symptoms to appear.
Note: Cobalt is actually necessary for our body (in small amounts) in the form of Vitamin B12.