You’ve probably been contacted by Google-based companies like Sedo, DomainSponsor, or NameDrive with a warning that domains you have listed with URL forwarding will no longer work after October 1st. This is something that Google has instituted, not these individual parking companies. Since Google-based services still seem to be paying better in general, it is probably a good idea to change how you direct traffic to these services ASAP.
This move seems to be another attempt at fraud prevention. Google can better track exactly where traffic is coming from if it is not forwarded from another source.
This change can be a pain for owners of multiple domains. One suggestion – look into bulk tools that may be available through your control panel. Enom, for example, allows you to create a “magic folder” that will change nameservers for every domain in that folder. This is one of the quickest way to make this change across a large number of domains. (Thanks to Eric Rice for inventing Magic Folders at BulkRegister which was bought by eNom.)