I have some hope for the iPad going forward but, for the moment at least, it is critically limited. I usually use my iPad only to watch streaming video and listen to recorded books. Every one of the Web browsers available for it is limited to one degree or another so I almost always find myself going to a real computer when I want to surf the Web. The iPad's primitive mail client is brutally hard to use and is almost unconfigurable compared to Mail and other genuine mail clients. Maybe iOS 4.0 for iPad will make it more functional, I hope so.
I recall you spent some time with a 13" MBP a while back and liked it. Do you prefer a larger screen size more, like your 17" for your main notebook or could you drop down to a 15 or 13", for example if a new suitable MacBook Air came out?
Going to a 13" from a larger screen can be a bit of a shock, especially more noticeable to me lately when I'm not hooking up to my 24" ACD as often.