An iPad has productivity apps such as Pages, Numbers, Keynote, Word, Excel, PowerPoint. You can even hook a keyboard up to it. However, if your going to be doing a lot of work on those apps or a lot of work your accustom to using on your desktop the iPad is not a good replacement. Its more of a tablet that has the ability to run the apps pretty well, but its still not a full OS experience so things will be harder to do and still somewhat limited.
But its really depending on what you are trying to do. What are you trying to do? Photos? Word? any kind of editing, if so what kind. The iPad can be a very good tool but so can a laptop. You just need to make sure you have the right one for the job.