"My wife is a college student and will be using this for school. What are some major differences between a laptop and the iPad. What are the pros and cons to having one versus the other assuming you had to pick between them?"
I am a student in college as well, going into my 4th year, and i've had the iPad since it was released, and was using for the second half of my second semester.
First and foremost, before addressing the issue of what your wife needs/wants in an iPad, you need to remember: an iPad is not a replacement for a fully functional laptop, or a tablet, or a netbook, or giant iPod Touch. It is an iPad, in its own market niche, and must be regarded as such. Don't expect things that the iPad was not designed for
Moving on. In terms of word documents, excel spreadsheets, powerpoints, etc, you can always get the three major apps that Apple sells for the iPad: Pages, Numbers, and Keynote. I currently have all three, and I'm very pleased with the results.
The ability to use landscape mode for typing is a big plus, since it becomes a fairly large keyboard, but some of the toolbars are a little harder to access in landscape, just a heads up. Otherwise, it is very useful, and I've been taking plenty of notes in class, and I've had no problem keeping up with the professors. Plus, people are amazed that you bring an iPad to class
However, if your wife needs to type up a paper or an essay, or maybe even a thesis, I would stray away from an iPad. It becomes too tedious, especially when you want to edit large chunks of your paper or when you want to quickly move things around. The lack of shortcut commands (copy, paste) while typing slows you down, so in this situation, a laptop or a PC would be more benefitial and less time consuming.
The iPad is pretty handy when it comes to reading books and pdfs, since it's so much zippier with a touchscreen, so that's always a plus.
As for storing files and such, there are many ways to turn your iPad into a giant portable device, but as said previously, you might be able to visibly move and control them on the iPad itself.
From what you've told us, it sounds like a laptop would be a better choice for you wife. A MBP or a Macbook sound like viable options.
If I didn't have a laptop/PC/etc., I wouldn't be using my iPad as my first choice. I already have a laptop, as well as a PC, so the iPad was just a nifty tool that is very reliable, handy, and fun to use. Like I said, do not confuse an iPad for a replacement for a laptop.
Hope this helps.