For residential use, for users currently requesting one public address, that's a waste of a /30 block (sans routing tricks requiring higher end customer equipment). Multiply that by the number of residential customers you have and that's bordering on mismanagement of your address space.
If you're dealing with business customers, then your usage versus wasted ratio is much higher and less of a concern, but what's the point? Are you trying to cut down on a large broadcast domain?
Any rational layer 2 access gear regardless of the technology (DSL, FTTx, wireless, or DOCSIS) will/can handle layer 2 isolation already. -- Scott Helms Vice President of Technology ISP Alliance, Inc. DBA ZCorum (678) 507-5000 -------------------------------- http://twitter.com/kscotthelms --------------------------------