> So that leaves concurrency inside applications and that just isn't something that affects most of the end users. There really isn't much for a word processor

> So that leaves concurrency inside applications and that just isn't something that affects most of the end users. There really isn't much for a word processor to actually do while the user is thinking about which key to press so it can do those few things that there was not time for during the keypress. This obviously depends on the application. Whenever you need to wait for an app to finish an operation that is not related to I/O, there is some potential for improvement. If a CPU-bound operation makes you wait for more than, say, a minute, it's almost definitely a candidate for optimization. Whether multithreading is a good solution or not depends on each case - when you need to communicate/lock a lot, it might not make sense. A good part of the solution is figuring out if it makes sense, how to partition the work etc.; the other part of this hard work is implementing and debugging it.