Greylisting specific IP ranges

[Bryan Scott]

Since my mail servers' users mainly deal with other North American users, I'd 
like to implement greylisting for specific /8's so I get some of the benefits 
of greylisting without the appearance of affecting users' normal email.

Has anybody already modified the greylisting plugin to be on or off for 
specific netblocks, or figured out a good combination of plugins that would 
accomplish this?

As a side note, I'm really leaning towards Gavin's per-user setup too, as too 
many of my users are complaining that my rules are either too strict or not 
strict enough.  Any gotchas with 0.32x?

-- Bryan