Coding Horror: Should All Developers Have Manycore CPUs?: "Here's the second part of the answer I promised you earlier. The one you might not like. Most developers aren't writing desktop applications today. They're writing web applications. Many of them may be writing in scripting languages that aren't compiled, but interpreted, like Ruby or Python or PHP. Heck, they're probably not even threaded. And yet this code somehow achieves massive levels of concurrency, scales to huge workloads, and drives some of the largest websites on the internet. All that, without thinking one iota about concurrency, threading, or reentrancy. It's sort of magical, if you think about it."
Read the entire article. It is a fairly accurate view in my opinion. However, and some of the comments point this out, while one application may not use all the cores, the other cores can be used for other applications.