Frank
These are interesting issues, but really unrelated to the definition of an interface for the search package. These are important issues to consider for the implementation of a specific search driver.
Re: OpenaACS.org, due to a silly bug on my part in developing the tsearch2-driver, the results were ordered in reverse relevance order, with the least relevant result first. This has been fixed for months now thanks to Jeff Davis.
Tsearch2 by default does stemming, and support multiple language dictionaries, but does not do proximity, I still think it returns pretty good results now. They results on OpenACS.org are much better than with the OpenFTS based search. One thing that would make it better is forums only search, for example.
THanks for your insights, we will definitely keep this in mind. The reason to support multiple search drivers is to allow more flexibility in how search is done.
