It's true, JavaScript is everywhere and that is the #1 reason I gravitate to it. As far as technical purity and niceness it's not the best, but there are worse languages that are widely used. I use CoffeeScript instead of JavaScript whenever possible, and this makes it very nice and almost Ruby-like.

Using it on the server side is the ideal situation for web apps, IMO, since you can share a lot of code between the layers. It's also quite fast for a dynamic language, because of all the focus JS performance has gotten over the years and servers benefit from that too. With MongoDB you can have JS in the data layer as well. It's great stuff really, I'd like to see more JS on the server over time.