I, too, would love to find out how to prepare...
I went to visit Waterloo this past November, and the tour guide told me all about it. It's some article written a long time ago apparently, in 'philosophy prose.' Whatever that means...
It sounds pretty scary. I guess your best bet is to read some difficult articles and to practice summarizing.

All I can say is don't worry. If your portfolio is strong, you're more than likely to get admitted. The only advice I can give is learn how to summarize and write an argumentative essay. When I took my precis test, I was certain I wouldn't get in as the paragraph we were given to read was extremely difficult. After we got admitted, and during the school term, our class was told that we had all failed the precis horribly, and the only reason we got picked was because we wrote our paper creatively.. :P

This doesn't address your question, but from what I hear, they ask you a lot of questions about your portfolio in the interview. So make sure you are on your game about what you put in your portfolio.

I live in Waterloo, so if anyone needs any advice on what to do, where to stay, etc. let me know.

Good luck too.

Anybody have any other examples or pieces they'd suggest to practice? Anything else that would help? The precis is soon... :(

What type of text did you have for a précis when you applied? What text was it? What was the author?

How can you write an argumentative essay if in a précis you are not supposed to present your own opinion? 

I do remember being told that although most of us failed badly in the precis.. that the scores you receive still play a role in if you get admitted.  You basically have to pass each hurdle they throw at you. You just need to make sure you're "cumulative score" from your interview and precis leave you in the higher percentile out of all the applicants.

I was on the interview panel for admissions almost two years ago now..I don't believe much has changed since. 

In terms of precis prep, my advice is just to read, and to make sure you understand what you are reading.  The topics have varied every year and it's really hard to study a certain way for a test that is basically different every year.