Search on Groups (based on profile manager created fields)?

@domblue: I have implemented solr search on my site. My implemetation is not that detailed. I manage most of configurations via the solr.conf and do not have the detailed interface as you mention. Anyway count me in on the effort, I can gladly help in my spare time.

I think elgg is a great platform but lacks heavily on the search aspect. The database structure is not at all search friendly specially the metadata.  For me, the native elgg search is way too slow plus the custom profile field search wasn't working properly a while ago. I tried all the above solutions like mysql native search, sphinx but they were not where close to solr's performance. 

Have you considered elasticsearch? I think it might fit in better than solr for elgg. 

@All: ElasticSearch, yes it is really cool to have. We are using elasticsearch + elgg from last 1.5 years. I believe, elasticsearch dynamic document model is best fit with EAV model of elgg. Where each entity could have different attributes to define the state of the object. Even though the object is of same type. And correspondingly elasticsearch document model fully support this behavior. We are using this model succesfully for more than 2 million entities. Best this about elasticsearch, we can scale up and down anytime we need and it automatically handle all internal complications like to identify the cluster, To work as replica for other shards, and many more advantages of elasticsearch.