There have been literally dozens of threads around here comparing AW and Sager.
The current Area-51m on AW's webpage is identical to the 5670. AW gives you a paint job, and some options are cheaper (like the 7K60 HD), but the base cost is so much higher than the 5670 that the AW will always come out more expensive.
The new Area-51m, confusingly with the same name, is currently only available for sale on eBay.
Current bid is $4250... (They're auctioning off the first machine as a promotion - check the bid history to find a familiar name...). If you note the machine's specs, you'll note that they do not match with a lot of the implausible specs previously posted here under said name.
The new AW doesn't appear to support HT (event though it uses the same proc as the 5680), and it doesn't support dual-channel RAM. It's RAM is PC2700 instead of the PC3200 found in the 5680. The AW's only advatages are the magnesium chassis and conforming video card (this makes it more likely the video card can be upgraded in the future without upgrading the mobo at the same time, which can save some money on the upgrade). Pricing on the new AW has not been released, but based on previous model comparisons will likely be significantly higher than the 5680.
So, the 5680 will blow away the New Area-51m in performance (HT, faster dual-channel RAM). The AW still uses a desktop CPU, so the 8600 will blow it away in battery life and weight. Hardly the "best of both worlds". As for cheap... well, maybe compared to the Dell.
Edit: After I wrote this I read a post with an AW ad
that indicates the New Area-51m does
have HT. So maybe it's just the model they're auctioning off that dosn't have it.