We see countless laptops come and go through the seasons, but a rare few have built up something of a following. Make no mistake: the Sony VAIO Z, a skinny ultraportable brimming with cutting-edge technology and powerful innards, is that kind of gem. So when it disappeared from Sony's online store earlier this year, more than a few techies took note. After all, the Z is part of a small fraternity of notebooks that combine an impossibly lightweight design with performance worthy of a larger system. People who missed out on the last-gen Z wondered when they'd next get the chance to buy, while some lucky folks out there with thousands to burn started itching for somethin