While there is currently no specific cap on the amount of interest that can be deducted, there is a cap on the size of the mortgage indebtedness. Currently (2009), for those filing single, the cap in mortgage debt is $500,000 and for those filing jointly the cap is $1,000,000.

There is talk that the loan cap will no longer be the simple, national $500k/$1M limit it is now, but like an FHA loan will vary city by city, depending on local housing costs. So the government may increase the cap in san francisco to say $1.5M for a joint filer and decrease the cap to $600,000 in Boise, as the cost of housing varies greatly between the two cities. 

Since a second home's interest is also tax deducatable do I get to take on another $1,000,000 in mortgage debt and deduct the interest from that as well?

Nope, the Mortgage Interest Deduction Cap is a total amount across both first and second homes.  

Heloc's are also capped at $50k for a single filer and $100k for a joint.