I didn't think it was a very good deal at the time since you can get a $99 EVO on-contract without trading in an old phone elsewhere (e.g., Amazon Wireless), but now that Radio Shack has cut the value of the old phone in half, I'm thinking that the old offer wasn't so bad after all.
Now when people bring in a fully functional phone that has no signs of liquid damage and has no cracked or broken parts, the Shack will let them use it as $50 toward a new HTC EVO or EVO Shift 4G.
The current in-store price of the EVO is $199.99, so those who walk into a Radio Shack with an eligible old phone can walk out of it with a brand new EVO for $149.99. That's better than paying the full price, sure, but the company is actually already selling the handset for $149.99 online without the trade-in right now. And don't forget that it's also been among the retailers that have sold the EVO for $99 (also without a trade-in) before too.