Rainer Joswig (the guy who hosts the screenshots) did live demos with his machines at the "5. Hamburg Lispers Meeting" in 2008 at my company's office. Here are some photos of the machines and the event http://www.flickr.com/photos/srichter/sets/72157605318306397...
The SLIME REPL is very much modeled after the Symbolics REPL. I guess Rainer can tell more about that. Check out the videos on his main site (sorry Rainer, this may increase traffic again. :) ).
The most amazing part of his demo for me was, when he inspected a running Lisp process, changed the code and continued from there. The OS is (almost) completely written in Lisp, too...
We have build a large Web-Application with Clojure. It runs on Google App Engine and we are really happy with our decision. You can find it here: http://the-deadline.com
We use the power of lisp to extend the language for specific tasks, like accessing the distributed key/value datastore or building an expert-system shell.
We can definitly recommend Google App Engine. The SDK is really cool and you don't have to care about managing servers. Scaling is easy. Its (almost) automatic. The datastore is a natural fit for Clojure datastructures, but you have to learn how to structure your data for a distributed key-value store: When you structure your data, you have to think about what has to be in the same transaction (entity-group) and at the same time you have to think about reducing data-dependencies to minimize contention. But when you have lots of data, this is what you have to do anyway. For me, it is much more fun than using an RDBMS. (Read this: http://code.google.com/intl/de-DE/appengine/docs/python/data...)
We did the whole system in Clojure, so you really can write large systems using Clojure/GAE. It works! (Although the UI is simple, TheDeadline is a complex piece of software e.g. containing a self-written rule-based expert-system, a production system, very similar to LISA http://lisa.sourceforge.net/.)
The functional paradigm means less code and makes it easier to build powerful abstractions. You don't have to write lots of boiler-plate code like in Java and Clojure is more concises and much more powerful than Python. (Stop! I don't want to start a programming language discussion now! :) ).
We will soon post some Clojure examples and some free software libraries for GAE.
The SLIME REPL is very much modeled after the Symbolics REPL. I guess Rainer can tell more about that. Check out the videos on his main site (sorry Rainer, this may increase traffic again. :) ). The most amazing part of his demo for me was, when he inspected a running Lisp process, changed the code and continued from there. The OS is (almost) completely written in Lisp, too...