Actors, multiple cores and Android

I'm about to start using Scala in a project which could benefit from
parallel processing, so naturally actors would seem like a great fit.
There are some things about them that confuse me, though.

First, use of multiple cores is one benefit often stressed when working
with actors. Do I need to do anything differently in my code to do this,
or does use of actors dynamically and automatically scale across CPUs?
Are there any styles of actor use that lend themselves better to
parallel processing? I'm guessing that splitting a task into smaller,
well-defined jobs is good, as each actor could then be assigned its own
resources across multiple cores.

Second, do all actor implementations scale based on number of cores? I
like Lift's actors for their simplicity, so would rather use those than
the default library.

Finally, do actors and parallel collections play well with the new
multi-core Android phones? I would imagine that there's no difference
between scaling across cores on a PC vs. doing the same on an Android
device, but I've certainly been bitten by unexpected differences before.

Thanks.