Sorry for the cross-post but I think it's relevant to this thread too. Found this re: UPX fare change:
http://www.metrolinx.com/en/projectsandprograms/upexpress/youchoose/go.aspx
Where do I tap on/off?
From Bloor or Weston
For travel between Bloor, Weston and Toronto’s Union Station, continue to tap on and/or off on the PRESTO fare payment device. Once you’ve tapped on, you can decide whether you want to take GO Transit or UP Express. You’ll continue to get your loyalty discount as long as your tap ON/OFF on the GO Transit PRESTO fare payment device.
Also:
*For a short period, while we implement technological changes, there will be a slight difference between GO and UP fares between Bloor and Weston GO Stations. A thirty five cent ($0.35) difference will be eliminated later this spring when the GO fares at these two stations are adjusted.