I find it to be oddly compelling, but I suspect that a 20" iMac with a UPS in an iLugger case would be smaller and lighter.
No subwoofer, though. The Dell would win there. I loves me some deep thumpin' bass when I'm sittin' in the cubicle at work with my homies.
If it were me, though, and I wanted a gaming PC, I'd buy a nice desktop, a decent 24" monitor, and a nice generator, then pay some kid to lug it around for me. I think it'd be easier and cheaper, and the carbon monoxide from the generator would really help me win against my non-oxygen-mask-wearing LAN party foes.