It's not very useful in Scala and thus not widely used. In general, you can use a symbol where you'd like to designate an identifier.
For example, the reflection invocation feature which was planned for 2.8.0 used the syntax obj o 'method(arg1, arg2) where 'o' was a method added to Any and Symbol was added the method apply(Any*) (both with 'pimp my library').
Another example could be if you want to create an easier way to create HTML documents, then instead of using "div" to designate an element you'd write 'div. Then one can imagine adding operators to Symbol to make syntactic sugar for creating elements
