Personally I really dig these numbered circles. I like it better than using letters. And I don't think it would look good with TTC font, although it would help if someone could mock it up (I can't unfortunately).
It was revised during the tenure of Adam Giambrone as Chair of the TTC, from December 1, 2006 to December 1, 2010. He was succeeded by Karen Stintz. The revision was a good improvement of the original. However, it can be better.
Is it me or is it that the Toyota Corolla ads still show up in slides 18 and 19 of the TTC customer service slideshow? I wonder how much money did Toyota paid to revamp wayfinding in the TTC.
By the way, the new colours have been unveiled: 5 as orange (Eglinton-Crosstown), 6 as grey (Sheppard East LRT), and 7 as light green (Finch West LRT).