I agree that there is a consensus. I disagree with the consensus, and would urge people to consider its potential, but I know I am in the minority
As a PhD candidate / lecturer /researcher I can vouch for its effectiveness in a rigorous and demanding academic environment. I would not recommend it as a replacement for a computer (I still use my Macbook Pro regularly for various tasks), but as a supplement. Most days, the iPad is all I need to bring to campus.
Your mileage will vary, of course, but I wouldn't dismiss it out of hand. In particular, anyone who does a lot of reading and handwritten notes will find it a powerful tool.
This gets us down in the weeds a bit but I think it's worth taking this whole question a bit deeper because it comes up a lot. Rather than try to decide generically whether an iPad is an adequate device for academic work perhaps a list of questions is worth asking.
() How good a typist are you? If you're a fast accurate typist, you'll probably never find a handwriting app that enables you to take notes as efficiently as you can with a keyboard. So factor that into both the costs and priorities. And if you're not a good typist, either improve your skills or invest the effort to be good with a handwriting app. If you're not willing to do either, keep a legal pad and a pen handy.
() Do you work regularly and extensively with PDF's provided for your classes? If so, an iPad with an app that enables pdf annotation can be a valuable tool. On the other hand, a laptop that enables you to view a pdf in one window and work in another may be a better alternative. In fact, depending on the size of a laptop screen, multiple resizable windows can be a valuable feature that you simply cannot duplicate with an iPad.
() Need to draw pictures/diagrams in addition to entering text? Here an iPad can be a valuable tool compared to a laptop. Drawing tools (often integrated with handwriting apps) can be very convenient.
() Need a long lasting battery? If you spend an entire day without access to an AC power source and/or don't want to carry a (sometimes brick-like) power converter, the iPad may be an economical choice. You can duplicate the iPad's battery with a laptop but it will cost you in terms of $$$ and additional weight.
() Need portable local storage? Apple thinks you don't. Yes, DropBox and iCloud can provide workarounds for many folks. But if it's important to have access to many large files even if you don't have access to wifi, don't count on an iPad. And the "walled garden" design of iOS may give you fits if you change a file in more than one application and find you have two unsynchronized files.
() Need sophisticated productivity applications, e.g. Office? Don't count on an iPad if the files are large or you use sophisticated features. The iPad versions of Apple's own apps (i.e. Numbers, Pages, Keynote) have fewer features than their Mac counterparts and even the Mac versions are less feature-laden than MS Office. Same is true for the various Office emulators for the iPad. Be careful.
All in all, I tend to agree with Palpatine that the iPad can be a valuable supplement for serious academic work, depending on the field of study and the complexity of one's particular requirements. If I had to choose only one device, it wouldn't be an iPad. But as an adjunct in a multi-computer configuration, it can be very convenient.
