I have programmed in Turbo Pascal, Basic, Visual Basic, Java, C, and Common Lisp (not that I got good at any of them). I would say that Lisp blows them all away in terms of thinking about a program through the tools of a progamming language. Its funny that when I talk to programmers trained on more popular language breeds, they can be either mystified by what I can accomplish, or annoyed by how I would accomplish something (Dont you know the standard? Your overcomplicating things, we dont need a server for this, just a command <that coincidentally might run a client to a program that runs on a local server>). There are different ways to the top of a mountain, so Im not saying that Lisp in an all powerfull abstraction of perfection. Far from it. Further, a project has good reason to keep itself compartmentalized to a language, mainly maintainability.
With Lisp, when I want to implement something that integrates with a system, I study the system, do exploratory programing, and really figure out how things work. I find that the main architecture of some of my more ambitious Lisp projects require accessing outside programs, so one of the topic I find interesting is IPC, perhaps born out of necessity. With PHP, I would look on the internet for the program that does the thing that I want and tweak it. Perhaps the power of Lisps core gives a fighting chance in these circumstances.
Another important point is that it is relatively hard to find Lisp programmers. This could be considered either a benefit (strategic advantage), or a cost (must overcome bigger hurdles for cooperative efforts).
I think its important to look at the advantages and disadvantages of using Lisp as a primary technology. Further, I think the disadvantages might be like opportunities in disguise. For example, using Lisp, you can design programs that could integrate with any another programming Language seemlessly (from a programmers perspective, maybe not from a system admin's perspective though).
This perspective is based on my very limited experience, and I am very curious about how experience guides in thinking about this topic. Im sure we all have alot to learn from eachother.