AnandTech and The TechReport have their reviews up. They like it. It’s a fast card, but it is a multi-GPU card and multi-GPU cards only flex their muscle with proper driver support. So if you’re willing to spend $549.99 USD and willing to deal with the fact that not all games will benefit from it, the AMD Radeon HD 4870 X2 is a prime choice.
Personally, I would still go for AMD’s Radeon HD 4850 — it’s a steal for the asking price of ~$169 CAD.