There's not much to say that hasn't already been said (ease of use, Plack integration). But I have been using Kelp for the past few weeks and enjoyed it so far. The fact you get a bare bones web framework with just the right amount of defaults is refreshing. If you need something else, it's easy to tack on with a module. If a module doesn't exist, it's very easy to write your own (I did in 25 lines of code) that added flash type functionality to my app.
Documentation is informative and nicely laid out. It's also available on the Kelp website with code highlighting.
Just remember the Kelp command line tool will not create the directory for you, only the structure. I fell for that one a couple of times and had to do a bit of cleaning up!