[Search] Order by Relevance: what are the mechanics behind it ?

Digital Doctor

Well-known member
Brogan reminded people about "Order by Relevance" as a search option recently.
I particularly like the Order By: Relevance option.
The feature seems interesting .. a few initial searches showed it *might* be a better method of searching than the default (I'll keep trying it).
I was surprised to see that "Order by Relevance" was disabled at: http://8wayrun.com/search/
Do you use Order by Relevance ?
What are you impressions with it ?
Anyone know how a search item's Relevance is determined ? {Q: is there a formula?}
Is order by Relevance harder on the server queries than order by Most Recent ?