It might not be the same segment, but the OEM that makes some of the various Apple products already has lighter notebook with SSD standard - the Asus Eee - sells for $300-400 right now depending on configuration - just under 2 lbs. Does everything an average computer would just more slowly. It can run Linux (default), Windows, or OSX(hacked). Easily user upgradeable to 2GB ram:
http://reviews.cnet.com/laptops/asus-eee-pc-4g/4505-3121_7-32466960.html?tag=prod.txt.1
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Description=asus+eee&x=0&y=0
http://reviews.cnet.com/laptops/asus-eee-pc-4g/4505-3121_7-32466960.html?tag=prod.txt.1
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Description=asus+eee&x=0&y=0