I suppose it depends on the type of person you are.
Personally, I find the iPad absolutely indispensable now.
If you are the type of person that has always sat down to the computer to do some serious work with some serious software, then your usual routine can in no way be replaced by the iPad....yet, although there are various ways in which it can add to it, connecting remotely (and mobilely) to your home, or other computers, for example. Also carrying a massive library of books with you and thousands of other gadgets in the form of apps.
I know an iPhone can do this and is much easier to pocket, but it's all just much more usable on the iPad due to the size.
If on the other hand (and there are many variations inbetween), you are more of a random surfer/researcher someone who wonders about a thousand things a minute, someone who just loves being able to answer their own questions by instantly being able to search and filter the millions of pages of information on the internet, watch videos, read information easily, then the iPad is great.
It's always by my side, it's simple, rarely goes wrong or needs any attention, and for me most importantly, doesn't require me to sit at a desk, I just cannot tolerate that position, with a big screen glaring in my face, I like the screen to be willing and able to move around me, not vice versa.
I love the big screen from a distance, but for general researching and basic computer tasks, iPad rules.