Acer and ASUS have unveiled new ultrabook systems. First up, the ASUS Zenbooks which is designed to up against Apple’s MacBook Air systems. The ASUS ultrabook comes in two flavors – The X21 that features an 11-inch screen and an i5 processor and 128GB SSD. The X21 weighs in at 2.2lbs, a shade under the 2.38lbs of the MacBook Air. Then there’s a higher-end UX31 which has a 13-inch screen, an i7 processor and 256GB SSD. Prices start at under $1,000, available starting October 12. Next up, the Acer S3 series ultrabook. This features a 13-inch display, i6 processor and a hybrid 20GB SSD/320GB HDD system and Intel HD 3000 graphics. This system has an attractive price tag, $899.99, a substantial saving compared to the MacBook Air’s $1,299.99 price tag. Should Apple be worried?