I think it is both old-time Lisp'ers and JVM platform programmers looking for something more agile than Java.

I have been using Clojure for my work for several months and for me some of the big wins are:

1. easy to use existing Java libraries

2. lots of nice language features like destructuring, etc.

3. nice integration with Java and/or Scala projects with IntelliJ

4. fairly good runtime performance

And, a few hassles:

1. error stack traces have relatively little value.

2. The Clojure team is doing great work, but I still feel that the platform is not quite there yet compared with Java, Common Lisp, Haskell, etc.

I am in a patient mood in regards to Clojure: I use it for some things now, and expect my percentage use of Clojure over other languages will steadily increase over the next few years.