Since word processing or just about the lightest thing you can do on a computer, it won't slow down. Even with MS Word, which is a sloooow behemoth.
That being said, I would'nt get it solely because of the keyboard. Too many hardware problems, and lack of travel, doesn't make it very nice if it is only used for word processing. Wait until they upgrade it, so it gets the 3. edition butterfly keyboard, or get the Macbook Air instead.