I read an interesting thread on CodeProject, one of the members was asking which language should he learn, PHP or Ruby? I think this is an interesting question from a more mature developer point of view. Most of the developers are familiar with at least 3-5 programming/scripting languages, but I think nowadays there is a bigger need to know as much as you can.
In the older days of computer programming there were developers who written nice little console applications, mostly in C. As the computer systems were increasing so as the requirement to create more complex and more robust applications had grown. There were (and today also are) back-end developers who focus on the back-end components of large systems, they know the business logic, they are familiar with the used data structures and the databases. On the other side, the front-end developers appeared, who were (and still are) trying to create client side software, as much as possible user friendly. I think the separation of the two type of developers did not appear only because of the different technologies used on the backend side and on the UI side; I think the thinking and the view of a developer defines where he/she should work. The back-end developers like to see all the details of the process, they like to see the data flowing through the system, they like to build the architecture of the system and I think most of them likes to help and support others.
The only drawback which can be mentioned is, that the newer technologies like Node.js are not adapted in the Enterprise market yet, but I can see that large corporations are embracing these new technologies, but they want to do this in a controlled and secure manner.