There's a lot of buzz about the MacBook Air lately, mostly bad. Everyone is wrong.
In the future, every Mac user will own three Apple devices. First, a Mac Pro or iMac. People who buy it themselves will usually get an iMac, while people who's business pays for it will usually get a Mac Pro. Secondly, they'll all have iPhones, natch. Thirdly, they'll all have MacBook Air's. And they'll all share the same data using .Mac, or something Google provides (Docs or Base or such), and it'll all be shared via your Time Capsul. Even over the Internet.
People's main computer will be their Desktop. When at home or work that's what they'll use. These will continue to use metal platter internal hard disk drives for the foreseeable future, possibly forever. HDD's are very cheap, and with ZFS you'll never lose data to corruption.
You'll also have of course your iPod. You won't have an iPhone because iPhones will be obsolete. In a few years iPods will have 120GB internal SSD and it'll be cheap. You can carry your entire music collection and plenty of movies with you on that device. If that's not enough space for you, just wait a couple of years until your iPod carries 8TB of SSD, instead of the 8GB it carries now. You'll also be able to do everything you used to do with your iPhone but it won't use AT&T's network. It'll use the 700Mhz spectrum that's going to be opened to every device. And it will be entirely Jabber/XMPP based. You won't call someone, you'll start an XMPP audio chat, but we'll still say we're making a phone call. You won't SMS someone, you'll send them an IM, but we'll still call it texting. It might not even have e-mail, in favor of XMPP. Every website worth it's salt will have a mobile version enhanced for small displays.
And finally for mobile computing you'll have your MacBook Air. In the future, all MacBooks will be Airs. They'll all have solid state drives. It won't matter that you can't carry a zillion songs, TV shows or movies on your Air because that will be on your iPhone synced from your desktop Mac. But then again, maybe you could, but you won't. You'll stream it over the Internet from your Desktop. You'll use your Air completely wirelessly, because at 5 hours of battery life for the first gen Air's with HDD's, you'll probably double or triple that with an SSD. The only time you'll need to plug it in is to charge it, the same as you do with your iPhone. The iPod first premiered with 5 hours of battery life and now goes for 44 hours of continuous playback.
You read it here first.
Update: More of what I'm talking about on 43 Folders.