It depends on which applications you are using.
Since the implementation of the multitasking feature, my iPad found new life and I appreciate it a whole lot more. After deciding that I needed a physical keyboard to appreciate it even more, I have found even more use out of my iPad than ever.
I am constantly writing articles that are of decent length, and replying to emails that need to have a pretty good description in them, in which the on-screen keyboard didn't cut it. After a while of typing, the on-screen keyboard would become slow at some times, but that is the only slow down I have noticed that was too bad.
If you do experience slow downs at all, just restart the iPad or delete all of the applications that are in queue for multitasking.