Been using it for just over a year. All the advice above is true. Don't forget about the freebees - they do expire.
One other thing I discovered by accident - is that customer service for unexpected situations is WAY better for corporate clients than normal people. We had some issues and were able to call the corporate line (someone answers very quickly), not the normal 1-800 number, and they actually HELPED with the situation, were FLEXIBLE, SOLVED the problem, and WAIVED some fees. For AC that is astonishing. We are going to continue to book all our tickets through the site - even though we don't hit $20,000 a year - just to maintain this service in case something goes wrong.
We also had the aeroplan name not matching problem:
Originally Posted by
ffsim
We've been set up with it since it launched. Tried using it but it insists my name doesn't match my Aeroplan number

Problem is the site needs your passport name - and it has to match your Aeroplan name as well. So, if your passport and aeroplan are different in any way - you have to call in. Quick fix is to change the way your name is in your Aeroplan account. Customer service was able to solve this for us in a few minutes. IT is apparently "working on it".