Silicone might be OK for hobby electronics but its use in professional electronics
(e.g. mil or space) is strictly controlled.
Silicone is not easy to clean and it can migrate to significant distance.
Silicone contamination of electrical contacts (e.g. relays and potentiometers) is
a big issue.
There are well known cases of enclosed relay contact contamination where silicone
passed throught the microcracks in packaging caused by wave soldering. These
effects show much later during the product lifecycle and cannot be detect in the initial
product testing.
Silicone also has negative impact during assembly (soldering, adhesive bonding,...)
In space and military electronics use of silicone is strictly controlled and limited. Just an
intersting example: NASA issued an alert regarding wristband silicone contamination (
http://www.spaceref.com/news/viewsr.html?pid=16511 ).