I think it's an awesome idea/concept, one which is arguably long overdue. I have a jailbroken iPhone 3G and a Dell XPS laptop. Love 'em both, but each has its limitations. I mainly use lappy for surfing Web, e-mail, IM, and viewing/managing photos & video. Use the iPhone as my main telephone, and for quick e-mail mgmt, surfing, and light texting, taking pics/video and gaming.
Part of the surfing is trading stocks/options and blogging on stocks/finance and, as one would expect, the Dell blows away iPhone in this regard. The quicker browsing speed, bigger screen, larger/full keyboard, and ability to view multiple windows on 1 screen is far superior to having to constantly swipe back & forth and resize on the iPhone.
I also hate composing or replying to e-mails on the iPhone; I love the multitap touchscreen in general, but the typing on a very small glass screen is a bit difficult for me.
Both are battery hogs, and while relatively lightweight/compact, the Dell is just cumbersome enough to make it a pain in the butt to haul around when I'm mobile. I do occasionally tether, but that's also a hassle and runs the risk of data overages with AT&T. I've considered getting a netbook, but don't want/need another flip-open device when I'm out & about, nor do I want to pay the extra $50-60/mo. in 3G data fees (am already paying for home cable Net service, plus the Iphone data fee).
So, for me, the Ipad seems like it just might be the ideal "bridge" device. I'm not going to rush out & buy one the moment it's available, as I'd like to see any initial bugs worked out and the price to come down.
But honestly, if it's half of what it's hyped up to be, and I eventually got one and fell in love with it, I'd consider ditching the Iphone and getting a Blackberry (or similar physical-keyboard smartphone) to use as my main phone and for mobile e-mail mgmt, texting, and light surfing. And, if the Ipad will offer MS Office & printing capability, and the ability to connect a CD/DVD drive & physical keyboard, I'd probably abandon the Dell as well !