Recently, I've become very intrigued with Ruby on Rails and how it can be used to VERY quickly develop very nice web applications.
I've had conversations with other people about why I would want to learn this, and interestingly enough, my responses were fairly similar to what Stephen Chu observes in his article titled 'Why would a .NET Programmer learn Ruby on Rails?'
In order to stay on top of your game as a developer, its going to be important to look at things outside of your comfort zone. Learning a new framework would certainly be one of those things. This is also right in line with what the Pragmatic Programmer book suggests by learning one new programming language a year. This helps broaden your thinking and avoids getting stuck in a rut.