Full text search starts on slide 32: http://www.slideshare.net/noloh/demystifying-postgresql
Even if you despise Java, SOLR or ElasticSearch aren't that hard to get up as a service. Each hour invested into getting those working is likely to return more value than an hour with PG's full-text search.
Let me define my own lexer as a UDF. Let me define a pipeline of filters like Solr. Let me use BM-25 text similarity like SQLite.
You can. CREATE TEXT SEARCH PARSER does essentially that. (Yes, it's called parser, not lexer, but in this case the difference essentially doesn't exist).
> Let me define a pipeline of filters like Solr.
Hm. Essentially that should be possible using dictionaries.
> Let me use BM-25 text similarity like SQLite.
Hm. It'll not be possible to write bm25 directly like in sqlite (matching to the current row without specifying it IIUC), but generally it's easy to define additional functions and use them for sorting and whatnot.
I think the postgres text search functionality unfortunately has lacked somebody with interest in developing it for a couple years now. It can be useful, but it could be much better. The default text search parser is pretty much useless in my opinion :(