Unlimited Marital Deduction Question

[Cara Lonsdale]

Can anyone break down the Unlimited Marital Deduction for me?

Spouses are both living, and still married.  Spouses file taxes jointly.  Both spouses are US citizens.

If Spouse A gives a CASH gift to Spouse B, is it a taxable event? 
How does it get deducted on Spouse A's taxes (what line)?
Does Spouse B have to report it (I assume so)?  If so, where (what line)?
What are the limitations, if any?

What else is important to know about the Unlimited Marital Deduction?