I use Cardpool to get electronic Target gift cards at a discount. They usually arrive in my in-box right away. Then I use them to buy the Disney gift cards on the Target site...and still get my 5% Red Card discount. I have never had the problem of the cards not being activated, but I have definitely heard of others having this problem.
When choosing my shipping method from Target.com, I always check the box saying that a signature is required. As someone previously mentioned, this ensures that the Target delivery comes via UPS and not USPS. I don't want $500 worth of gift cards sitting in my mailbox. No way. The gift cards also arrive much more quickly via UPS, and it's still free shipping.