I have 3 major complaints about actors (specifically Scala/Akka actors, but most of the models I've encountered have similar problems).
1) In general, I think that going parallel should be an architectural decision. On current commodity architectures it doesn't buy people as much as they think it does, and can in many cases over complicate code. Actors hide this complexity, but don't actually remove it. People think actors give them free license to add tons of threads when they shouldn't.
2) Actor code tends to mix business logic with threading logic, precisely what we should be trying to avoid.
3) The actor model subtly conflates publisher/consumer models which tend to decompose and perform better in parallel situations.
Normally, for calculation style parallelism I prefer future/promises and for event style parallelism I prefer single writer/multiple consumer based shared memory.
