Trailburn just finished a review of the new Giro Xar MTB helmet.
Here's two quotes from the review:
Thankfully, the research that goes into Giros helmets is second to none and they consistently have the more well constructed and fitting helmets on the market and the Xar lives up to this expectation.
it is really light and has a more svelte road-race type of feel to it. Aggressive and fast riders find comfort in beefy products and the Xar is on the XC side of aggressive riding helmets when wearing a full-faced helmet is not necessary or overkill for the style of riding.
Trailburn is giving four stars to the Xar.
To read the full review:
http://trailburn.ca/2011/04/27/giro-xar-review/