I haven't done any extended touring, just a week or so at a time, but I find my iPad does what I need. It doesn't mean it will suit the OP's needs, but for me, it's hard to imagine what the iPad can't do that I need to have done. Battery life, built in GPS and cellular data (if you opt for that model), large screen (compared to a netbook or smart phone) are all points in its favor.
If you're going to do a lot of typing, lack of a physical keyboard is a problem, but there are options for physical keyboards as well, and they range from compact keyboards that double as part of a case to full-sized keyboards. I tend to carry my regular bluetooth keyboard if I'm going to be away for any amount of time. I actually spend very little time sitting and typing, but when I find myself with time on my hands and e-mails to answer, the keyboard is nice to have. Still haven't determined if it's worth the extra space, though, for the amount of time that I use it.

There's plenty the iPad can't do that a "real" computer can, but there's plenty the iPad can do if you're willing to work with it. Even around the house I find that I seldom sit down at the computer anymore...except to sync my iPad. Every now and then a task comes up that requires the computer, but even then I sometimes just log in over the iPad. It's probably not a computer replacement for most folks, but then neither is a netbook. For touring, it's been a great tool.

I've used mine for:

• e-mail
• web surfing
• edit/upload photos from my camera
• watch movies in my tent and on the train
• games
• reading books and comics
• music/podcasts/audio books in my tent
• storing my route
• finding myself on a map (seriously, GPS+saved maps is my favourite thing about having the iPad on my bike)
• saving my route to share with friends/family.
• maps in general are great on the iPad. One app in particular saves pdf maps and, if they have the right data embedded, uses the GPS to show where you are on that map, like a campground map, for instance.
• Managing train tickets.
• finding near-by restaurants/grocery stores
• plus it makes a good-enough light source if you're in your tent and don't need full flashlight brightness.

It really has become one of favourite travel tools, on the bike or off. Maybe there is some key functionality that it lacks and a particular user might need, but for me it's been great. Worth looking into. Not for everyone, I know, but it's completely sated my desire for any laptop.