We're having a bit of an issue with DNS scavenging and accurate entries in the forward lookup zone.
Domain: Server 2008 R2 (Forest and Domain)
Scavenging: Enabled (7 days / 7 days)
Dynamic Updates: Enabled on DHCP server / No GPO pushing it out, default should automatically do it
We're seeing a lot of issues with dns records as far back as February of this year. Some machines are part of our domain, others aren't (personal PCs, Blackberry devices, iPhones, etc.) We also see multiple entries in forward and reverse zones.