Boos makes two different things for oiling boards, one is a mineral type substance and the other is more of a goopy honey wax type of stuff. Not sure what either of them are but both work really well.
I wash mine and hand dry and probably oil every month or so. I cut everything on them except stuff covered in certain spices which can cause serious staining. Even if they get stained I just sand them and apply more oil.
If any of you live in the midwest near Central IL be sure to stop by the Boos outlet in Effingham IL if you can. I've got 3 Boos boards and paid less than $60 total for all of them. A 18"X3" thick round end cut block, a 18"x12"x3" end cut maple block, and a standard 18"x12"x3" block. Last time I was home they had extra sections of 3" thick Boos Butcher Block counter tops for $10 a linear foot. If I could have got a 6' section on the plane I would have.