Dave Dugdale of Learning DSLR Video recently produced a terrific review of the new Panasonic GH4, which shoots 4K internally to SD cards. Since the majority of work is still being finished in 1080p, he's been downscaling most of the stuff he's shot to 1080p, but he wanted to explore the differences between downscaling in the timeline or after he's finished editing in a 4K timeline in Premiere. He also addresses people accusing him of being paid off by Panasonic for his review.
While you may not see any real differences if you're not doing much to the footage, the other advantage to working in a 1080p timeline with 4K footage is that you're able to crop or stabilize the frame however you need to and still end up with a high-quality 1080p result. At the moment this is one of the huge benefits to 4K, that you can do a lot to the image and retain detail for a beautiful 1080p finish. Even if you're not going to be showing your work in 4K, having that extra resolution to play around with can be extremely helpful.
Check out more over at Learning DSLR Video.