I'm involved in the development of an application using Solandra (Cassandra based Apache Solr). In my experience the system is quite stable and able to handle TB+ data. I'm personally quite happy with the software for the following reasons:
1. Automated partitioning of data due to Cassandra backend.
2. Rich querying capabilities (due to Solr and Lucene).
3. Fast read and writes (writes significantly faster than reads).
However currently Solandra, I believe does not support batch mutations. That is, I can insert 100 columns in a single insertion into Cassandra, however Solandra does not support this.
