The VAIO, as an ultraportable machine with long battery life, is impressive. The integrated DVD drive is a plus, too. A Sony Vaio IS TINY by definition (not designed for huge fingers).
The MacBook Air, on the other hand, will be an impressively portable, basically-full-size computer. It won’t feel small and tiny like the VAIO but it likely won’t weigh you down much (about 1.5 kg) either. Both laptops have similar perfomances based on Corel 2 Duo processors with some advantage for MacBook. Same happens with RAM: Apple’s comes with 2GB of 667MHz DDR2 SDRAM. Sony’s comes with 1GB of 533MHz DDR2 SDRAM.
Finally, Sony’s site has the VAIO listed at $2099. You can currently get it at Best Buy for $1849. The MacBook Air is $1799, launch price.