Based on a 40nm GPU codenamed "Redwood," the card's specifications include 400 stream processors operating at a clock frequency of 775MHz, offering more than 600 TeraFLOPS of raw computing power, and either 512 ($99) or 1GB ($119) of GDDR5 memory for a total bandwidth of up to 64 GB/s on a 128-bit bus. In terms of energy consumption, the single-slot Radeon HD 5670 offers an impressively power low draw of just 14W at idle and 61W under load.
The new card is said to consistently outperform Nvidia's GeForce GT 240, which was already an irrelevant product anyway, but since Nvidia is pricing it at $99 that's what AMD is positioning its 5670 after. Overall you can expect most games to run smoothly at 1680x1050 with anti-aliasing and detail levels cranked up. Check out some reviews at PC Per, Legit Reviews and Anandtech.