How bad are ast and boca boards, how much do they put load on the system ?

They're about equivalent to just having multiple 16550s, with the sole
exception that they can share an interrupt line.  If you wouldn't
consider using five 16550 UARTs, then an AST or BOCA card wouldn't buy
you anything.

   Has anyone experimented writing digiboard driver for NetBSD ? There seems
   to be Linux driver that one could use as a hw-docs, would it catch the
   gnu-public virus that way ? 

A driver for the *programmable* DigiBoard cards would be nice, but you
can't get programmings specs without a NDA.  Is the Linux driver for
the `dumb' or `smart' boards?