Events are not only an alternative to threads they are also a complement. If your language environment has a complex memory model with good concurrency support and stable non-blocking IO, you can use threads! But for them to be good you need to make sure that the input and output is compatible, as a general guide:

1) Make sure your hardware interface is capable of being accessed by the kernel from multiple threads. Network cards generally allow this, while graphics cards still don't, at least without a lot of overhead.

2) Make sure your application profits form parallelism, and specifically joint parallelism; which is my term for computing that allows many threads to work on the same memory.

Bottom line is in my case only the Java server for my MMO will use threads in a "joint parallel" way. In everything else I will avoid them like a jerrycan full of gas tries to avoid fire.

So I'm transitioning to C with arrays!