I think the conclusion I'm reaching is that my boss is a good candidate for both an iPad and a light-weight laptop. I expect that he will be somewhat disappointed with the email and remote access functionality on the iPad. You don't expect a die-hard Outlook addict to actually like iPad's limited email app, do you? I understand you can only view the last 250 emails. My boss is accustomed to searching 10 gigs of email.
The iPad will work great for new emails that come in, reading eBooks, browsing the web, etc. But when he really wants to get down and work he'll just simply have to dig out a light-weight Windows laptop.
As far as light-weight laptops go, I have my eye on the Toshiba Portege 830. It's not cheap and the whole solution of buying both for sure isn't, but I'm going to try to convince him that this is probably the only way we'll meet all of his needs.