TechCrunch found a virtual world service (think Second Life) called LivePlace, which aims to render very realistic environments in real time by rendering it first, then pushing image data to devices. The service is supposedly working off of a service from OTOY which specializes in server-side graphics. In the case of LivePlace, you'll be using that pre-rendered "massive" cityscape to walk your avatar around in.
What's great about this tech is that because they render all this stuff serverside, this beautiful imagery can be streamed to even the crappiest of devices. Case in point, the leaked video above was shown on a Treo 700 at 240kbps while being rendered somewhere else. Hotness doesn't begin to describe something of this quality that can then be customized to your liking. [TechCrunch - Thanks Ariel!]