The Kindle is great for reading books, in any light and its lightweight for travel. If that is primarily what you want go for it.
The iPad is really an emerging device. It is designed to view, rather than create content (although it does that to some limited degree). The big advantage of an ipad over a mac book or a PC are:
a) it sealed so you don't have to separate it from your luggage in airports (although I'm sure different lines, different rules)
b) instant on
c) lightweight, but not as light as a Kindle
d) richer screen -- better for magazines and newspapers than Kindle
e) ease of use
I see it as an in between machine. Now I can travel for a couple of days with just a smart phone. If I need a little more horsepower with me to do different things, I will go with the pad -- I can access all of my corporate files through the browser. If I need to do real work, out comes the PC. But I'm a "tool junky". You should note that I also have about 6 different brief cases.