PHP vs Rails vs obj C vs scala
spooneybarger: If you want to add to your skill set, I would think you have a couple possible motivations...motivation a- expand the mind.If that is the case and you know c/c++, I would say, go with scala as it is the farthest afield from what you already know.motivation b- develop a marketable skill.If that is the case, then I've always been of the opinion that it is better to develop skills that others don't have. 
If you learn PHP, you've learned a commodity skill. If you learn scala, you are in a select few for the time being and although their might be fewer jobs, there will also be less competition for them and you can probably charge more. I don't know what the going rate for Rails developers is now but a couple years ago, it was crazy high because the demand outstripped the supply.