Rode the subway extension for the first time last night. I was pretty impressed, it looks fairly well used and took about 45 mins from VMC to Union. VMC station has a long underground connection to the KPMG tower but on a cold night like last night at least keeps you inside away from the elements longer.
A few observations I made on my return trip around 10:30 pm
Downsview park station - very few passengers here, as mentioned this station appears to be dependent on connections with the Go station.
Finch West station - About a dozen or more passengers boarding/disembarking this station
York University station - Only a couple of passengers boarding/disembarking this station, I suspect this was not prime University student hours for this station
Pioneer Village station - About half a dozen, or more passengers boarding/disembarking this station
407 station - More than a dozen passengers boarding/disembarking this station. Presumably they are using the parking lot and coming in on the 407 from the East and West
VMC station - Well over 30 passengers disembarking here. The PPUD area was filled with cars waiting to pick up passengers and the parking lots (now charging a flat rate of $5) was about 40% full.
So while not a smashing success I would say the extension is getting some usage, and the area around VMC station seems to be coming along nicely. I note that there was a Toronto Raptors game last night and many of the passengers were coming from the game, however I suspect that Blue Jays game nights, Concerts, etc will see the same levels of usage (It's my experience that Maple Leafs games have the lowest level of transit usage so I do not include them) if not more so.