We had a similar discussion a long while ago (2 years?) on whether having RFC1918 addressed router interface could break Path MTU discovery.
The general upshot is that the RFC specifically says that no packets with a reserved address in the header (source or destination) should leave the network in question. Also, the RFC says it is not at all unreasonable (but not required) for a network to filter packets with RFC1918 addresses in the source. (To prevent attacks and things like that.)
So it is nearly impossible to stay 100% compliant and address router interfaces with RFC1918 addresses. (Unless you NAT or something.)
Of course, if you use RFC1918 space for internal addressing, then filter all RFC1918 SA both ingress _and egress to your network, you'd in theory be 100% compliant (whatever that means). You'd just be handicapping traceroute, PMTU and the like .. but of course, if folks have a problem with it :-) -danny