I was using Skype on my Windows 10 PC the other day. Early on we talked about what films we might want to see soon and the new Pirates of the Caribbean movie was mentioned. Less than half a minute later an ad came up on the Skype window - an ad for the new Pirates of the Caribbean. I thought it was spooky.
We didn't text each other before or during the Skype session, so there must have been speech recognition involved, unless someone was listening and maybe joking with us. My Skype partner was using an iPad or iPhone and saw no ad. Neither of us had the Skype video enabled.
Reading my Gmail I've seen ads that show up in the mail window, which relate to the contents of the mail. It feels less harmful. The Skype "incident" was new to me. A phone call, albeit on Skype, is more intimate than email and the ad felt consequently more intrusive. I didn't like the experience.
There is but a small step from popping up ads to actual spying. From this I learned that I need to watch my words while Skyping. I'm convinced that this could happen on any service, but Skype is the first service that demonstrated its use to me. Thanks Skype!