DKIM checking but not signing with Postfix?

[VR]

My Debian(Lenny)/Postfix environment is inbound only (except 
bounces/rejects of course) that uses transports to hand messages off to 
Exchange servers for multiple domains.

I've been reading about DKIM in the Postfix archives most of tonight and 
have seen both praise and pause going back to about 2007 regarding 
implementing DKIM in general.

I realize DKIM, nor Postfix are "spam solutions" but I would like to 
know if DKIM might reduce the number of forgeries passed through my 
Postfix gateway?  More specifically, from hosts claiming to be larger 
organizations that do use DKIM signing for their outbound traffic?

Ideally I would not like to do content inspection (at this time) nor 
would I like to implement outbound signing. I have seen some write ups 
on DKIM but all discuss signing outbound.  Can DKIM be done just for 
inbound?  And which DKIM implementation works smoothly or is recommended 
with Postfix?