Floating point values are not supported in Sphinx versions below 0.9.8.
With regard to synonyms, Shodan states “these rules are tokenizing exceptions; they can only be applied at indexing time. So reindexing is required.”
No.
Yes. At the moment it is only able to pick up new index data in runtime, but not the configuration settings. This is going to be fixed in the future.
Note for 0.9.9: indexer saves index setting inside index files so you don't need to restart searchd after –rotate.
Yes, with software like logrotate you can rotate the query log as long as you send searchd SIGUSR1. See Tips and tricks.
This is actually a question on MySQL client library. Typically, it will attempt UNIX socket connection over sql_sock when the host is “localhost”, and TCP socket connection to sql_host:sql_port in all other cases.
(details?)