I run an iMac and and IBook at home and (due to the corp policy) a Toshiba portege for work. The portege is super light with an excellent keyboard and doesn't come with a CD/DVD drive - but I don't want one on the road.

If I want a machine I need to watch a DVD on, or my small child needs to watch a DVD on, I take the bulkier iBook.

My dream machine would be a light apple accepted by the corporate purchasing gods.