The old site search was broken and dying, as it tried to keep a database table of every word ever used while matching it to every post that ever used the word. So the new site search we make is going to be done right (able to scale to our size) and will take us a while to get around to.
For now, we have made available a third party site search feature from Google. It can be found in the header of every page now and can find users and topics but doesn’t do well at finding specific posts or in limiting the search by date or user as it is a general web page search and doesn’t use the database fields.
A real site search engine will eventually be built that will handle more powerful searches for specific posts but is a bit low on our priorities at the moment.