Wow, a lot of activity on this thread today! Guess I picked the wrong day to take an internal company training class... anyway, I thought I'd chime in with what I've done and what I know...
Regarding the 400-character activity word limit... you are correct if you've noticed that Columbia's app counts more characters than Microsoft Word. I went with Microsoft Word's count. I know Columbia's app count is "safer" but to be honest, I don't think five or six characters will matter. The reason is because you can save and click on the "print my application" option on the bottom left toolbar. If you do this, it formats your entire app in the format that I suspect the Adcom uses to print out and package our apps in. You'll notice that the print-out format does not cut out words past 400 characters or anything like that. So the difference between 399 and 401 and even 410 is nearly zilch. The word limit was put in to keep applicants from writing every detail about their activities (according to Christina once again). They won't notice if you're slightly over the word count. I completely agree with abbreviating names though. For instance, Harvard University Beer Pong Team can be "Harvard Beer Pong."
Similarly, the word count for the essays are "recommended word limits", not hard and fast rules. I called the Adcom and they confirmed that they do NOT stop reading after a certain point nor do they know whether you've gone over. They said basically it is a recommendation and you can go over a little if you need to (they didn't clarify how much was okay but I do subscribe to the 10% rule like everyone else). If you do the same "print my application" trick above, you'll see how your essays look when they print it out and realize that the difference between 750 and 825 (aka 10% over) is about one small paragraph. Since we know the Adcom doesn't count words and doesn't stop reading at a certain point, there isn't really much of a difference when you're reading. I really think Columbia is one of the more lenient schools with regards to the essay limits so I wouldn't sweat 825 for Essay 1.
Sorry for the detailed analysis. Just my 2 cents
P.S. As for the "Have you spoken with CBS Representatives" question, I am going to call the Adcom tomorrow. I agree that Christina may have mis-spoke (or mis-typed) when she said that students are okay. Most of us have probably talked to many students already! I'll post whatever answer I get tomorrow.