The wiki at the top of this thread seems woefully out of date? Anyways, here is what I gathered from TD's website:

Additional cardholders receive:

• First year annual additional cardholder fee ($75 CAD) waived.
• First checked bag free (up to 23kg/50lb) when travel originates on an Air Canada flight.
• NEXUS application fee rebate (up to $100 CAD) once every 48 months.

Additional cardholders do not receive:

• Threshold Benefit: Aeroplan Elite Status Qualification Boost (for benefit of Primary Cardholder only) For every $10,000 in net purchases (less any returns and credits) charged to the credit card account, Primary Cardholders will receive 1,000 Status Qualifying Miles (SQM) and 1 Status Qualifying Segment (SQS), to be deposited in their Aeroplan member account at the end of the next credit card account billing period. Please allow up to 1 week after your credit card account statement date for the deposit to appear. SQM and SQS are not redeemable towards Aeroplan rewards and only count toward Aeroplan Elite Status qualification. SQM do not count towards Million Mile Status. Additional Cardholder(s) are not eligible to receive SQM or SQS through this benefit; however, all net spend by Additional Cardholder(s) will count towards the Primary Cardholder’s spend. The cardholder may earn unlimited bonus SQM and SQS during an Elite Status qualification period.

What I haven't been able to find, and maybe it's too obvious to require stating, is whether Aeroplan points earned through spend of the additional cardholder goes towards the primary or additional cardholder's Aeroplan account.