On the collection side of things, one of the first questions I saw was: do parallel collections share a common interface with standard collections. The answer is yes, they do, but not one that existed in 2.8.1.
You see, a trouble with parallel collections is that, now that they are available, people will probably be passing them around. If they could be passed to old code -- as it was briefly contemplated -- that old code could crash in mysterious ways. In fact, it happens with REPL itself.
For that reason, ALL of your code comes with a guarantee that it will only accept sequential collections. In other words, Iterable, Seq, Set, etc, they all now share a guarantee to be sequential, which means you cannot pass a parallel sequence to a method expecting Seq.
The parallel collections start with Par: ParIterable, ParSeq, ParSet and ParMap. No ParTraversable for now. These are guaranteed to be parallel. They can be found inside scala.collection.parallel, scala.collection.parallel.immutable, etc.
You can also get a parallel collection just by calling the ".par" method on it, and, similarly, the ".seq" method will return a sequential collection.
Now, if you want your code to not care whether it receives a parallel or sequential collection, you should prefix it with Gen: GenTraversable, GenIterable, GenSeq, etc. These can be either parallel or sequential.
And, now, something fun to try out:
def p[T](coll: collection.GenIterable[T]) = coll foreach println; p(1 to 20); p((1 to 20).par)