I really like most Asus stuff, but I can't believe how ugly the W5A is compared to other Asus models.
12" laptops seem to fall into 2 categories. Either they're ultraportable or they're not. The 700M, for example, isn't really lighter or thinner than a lot of 14" laptops out there, so you're getting a cramped keyboard and small screen on a laptop that isn't really that small. Others that are ultraportable are missing optical drives, have slow 1.8" hard drives, and have the ultra-low-voltage CPUs that are significantly slower than most laptops.
That Acer you linked looks very nice to me. It's only 3.1 lbs... I can't think of anything else that light with a good hard drive and good CPU. The CDRW is external, but there's really no avoiding that. Notice that it does have a decent amount of empty space around the screen and keyboard, though. Its dimensions are 11.7" x 8.3" x 1.3". The Latitude X1 also has a 12.1" screen, but its dimensions are 11.26" x 7.7" x 0.98".
It really depends on what you want to give up for the sake of portability. Having a small keyboard and a 12" screen is already giving up plenty, so you might want to go all the way and get something smaller like the X1.