Gustavo Fernades, Senior Open Source Consultant at Sourcesense UK, recently did a talk detailing six Solr tuning tips that can help significantly reduce query times in large-scale and near real time search environments. He covers adding memory,  auto warming, application profiling, FieldValueCache, JVM and garbage collection, and using maxWarmingSearchers.

Check out the video for more details:
http://vimeo.com/17402451