Yah, critical mass is coming. I think 2010 is a reasonable year to use as a benchmark of assessment for that. It's a little bit off yet. There is still a massive amount of space to fill and connections to make throughout downtown and Midtown to even start revealing a contiguous stream of livable space.
My prediction is that the time period between 2010 and 2015 might start to usher in the second phase of critical mass building, heavily dependent on two things: 1) the state of the economy, and 2) where we are with mass transit. This 5 year period might be used to build the first of a system and IF (big if) we have it by 2015, the 5 years thereafter could be the time period where greater downtown achieves signs of critical mass.
What you are seeing now is just the snowball effect of a few critical events that have occurred in the past few years, a few of those being Campus Martius, GM/Compuware, Riverfront, Book Cadillac, and streetscapes.
Thanks for the picture updates, sub. Now, I don't have to do it!