I've been working with ElasticSearch over the past months as part of the MetaCPAN project. Using ElasticSearch as our back end has worked out really well so far. The reason is that, out of the box, it provides a REST API. So, in our case, we've been able to concentrate on writing code and not on designing an API, defining its behaviour, arguing over URL schemes etc.
To be clear, ES is not written in Perl, but there is a handy Perl module you can use to get yourself up and running in *minutes*.