I've got one
I've been fairly pleased with my M11x, it certainly does play plenty of games at high detail settings without any real drawbacks. The facial recognition login is a fun if useless feature too.
My main complaint would be that many units (including mine) are unable to overclock thanks to the BIOS undervolting the CPU when overclocked. Apparently this is to help save battery life but the knock-on effect is that weaker chips are unstable. I should have returned mine but I was expecting Dell to knock out a simple BIOS update, which they haven't bothered with. Now that the i5/i7 model is out they'll likely not even bother now.
Still, even at stock it runs everything very well, with only CPU intensive RTS games being hampered by the low clocked 1.3GHz Core 2 Duo. Games like Mass Effect 2, Arkham Asylum, Mirror's Edge, SFIV, Devil May Cry 4, etc all run perfectly. You can tell from that list I basically use it as a portable Xbox 360, and it excels at that.
The timing of El Reg's review is a little odd considering the i5/i7 model has been out for a couple of days. It would be nice to see what sort of performance difference is to be gained by the new CPUs. Plus from what I understand the new model has Nvidia's Optimus onboard so you don't need to worry about switching GPUs for simple browsing tasks (I never bother with mine).