spoofing question

[Matt <mhersant_(_at_)_comcast_(_dot_)_net>]

A general security question about spoofing modern *nix operating 
systems, including OpenBSD.  Is spoofing pretty much dead?  Do modern 
*nix machines still use the old BSD style incrementation of sequence 
numbers (I don't know enough C to find it in the source)?  Or are 
sequence numbers now random (unspoofable).  Also, don't high speed LANs 
(gigabit, fibre) make it doubly hard to guess sequence number?  I 
couldn't find much on the subject.  Thanks.