OK I shelled out the hundred bucks for the annual subscription to Office 365 (And then two days later found it for $79 at Office Depot, sheesh!).
So far it seems to be worth the money if you need to edit or create documents on your iPad. If you only need to read docs, spreadsheets or review PowerPoints, just get the free versions and stick with them.
The nice thing about the annual subscription is that we can put Office on 5 computers AND 5 tablets. And it is supposed to always be up to date. So I now have access to Office 2013 pretty much everywhere I go. And with the free (somewhat crippled I will admit) versions of the Office apps on OneDrive on the web, I am in business as long as I can connect to the internet.
I have tried all the apps on my iPad and find them to be very well executed and easy to use. Track changes works just like on my desktop PC so that made it worth it for my wife who uses it all the time when reviewing dissertations for her students. And it works for me when I am editing files with my coworkers.
If you don't mind having to pay the annual subscription fee and you need to edit docs on the run and you don't want to have to drag a full sized laptop around with your, I would recommend getting the apps and paying the fee to activate Office 365.
The only con I have run across so far is that the Save As option to save a document to your iPad so you can work on it between internet connections is less than intuitive. You have to make a copy, not surprising, but the option to do this is called Duplicate rather than a simple and easy to understand, Save As.