Lua I'm having a little bit of trouble getting some traction with Lua. Its a relatively new language and doesn't have too many libraries or bindings in the Debian package archives. Since I rely upon Debian quite a bit, that makes a significant difference to me.
On the other hand, I do note that it is super fast. I've written a couple of shell scripts with it, and I've followed a few WSAPI tutorials for FastCGI.
I also rely quite heavily on XML and unfortunately I find the XML support in Lua to be really foreign. I just don't get it. I found a suggestion on some one's blog to transform XML into a Lua table using XSL and that actually worked really well! I may use that technique in Nexista instead of running SimpleXML functions over and over.
Perl I've really grown to like Perl. Its not the fastest language under the sun, but it is incredibly flexible and there are an incredible amount of libraries and modules out there.
I just built my first Catalyst application for a client of mine and it went very well. A decent user interface and database connectivity in under thirty minutes. Talk about rapid application development! I also learned that Catalyst has an XSLT view-module. That is very very good.
I've generally stayed away from MVC frameworks because they tend to avoid XML. I still plan to rely heavily on XML, but I'm impressed enough with Catalyst as an MVC to research more of them. I've tried Symfony and Ruby on Rails, so I want to try Orbit next - the Lua MVC framework.