Here's an incomplete list. Start counting:
1. a link to Reader was displayed in Gmail's inbox when there was no mail
2. for many years, Google Reader could be found in the main navigation bar, next to Gmail, Calendar and Google Docs
3. Google Reader was the first Google service that worked offline and the first Google service that used Google Gears, back in 2007
4. Google Reader integrated with Google Social Search, a feature that allowed you to restrict results to the pages written by your friends or people you follow.
5. iGoogle integrated with Google Reader when it started to add support for canvas view. Maximize a feed gadget and you get the Google Reader interface.
6. Blogger's Following feature was powered by Google Reader. "The blogs you follow in Blogger have been added as subscriptions in Google Reader. Subscriptions can be managed in Reader without affecting your following list in Blogger."
7. Listen, Google's podcast manager app for Android, used Google Reader to store subscriptions.
8. Google Alerts integrated with Google Reader, so you could subscribe to feeds instead of receiving email notofcations.
9. Back in 2008, Google's mobile transcoder displayed the site's feeds at the top of the page and linked to Google Reader.
10. Google Reader was the only Google product with an interface optimized for Nintendo Wii.
11. Google Currents, launched in 2011, allowed you to import your Google Reader subscriptions.
12. Google Buzz's commenting feature was integrated with Google Reader.
13. When Bloglines was discontinued in 2010, Google Reader's team encouraged users to switch to Reader. The blog post includes a graph of Reader users over time.
14. The Google Groups redesign from 2010 was inspired by Google Reader.
15. Google bought FeedBurner to monetize Google Reader and launched AdSense for Feeds.
16. Back in 2007, Google Reader made shared items available to Google Talk contacts and many people complained about this.
17. Google's Power Readers feature from 2008 allowed you to "track the news sites and blogs Barack Obama and John McCain read" using Google Reader. It was a clever way to promote Google Reader. This feature was expanded to "include journalists, techies, fashion critics, foodies and more".
18. Google Toolbar for IE allowed you to subscribe to feeds using iGoogle or Google Reader.
19. Google Blog Search still has this link below the list of search results page: "Subscribe to a blog search feed for [query] in Google Reader". Google News had a similar link.
20. Google Spreadsheets has a special function for importing feeds that was initially called GoogleReader. Now it's called ImportFeed.
21. Google TV Queue uses Google Reader to manage subscriptions.
22. Google Reader was Google's infrastructure for feeds and the technology was used by iGoogle, orkut, Gmail's web clips, Blogger widgets, Google Spreadsheets and the Ajax API.
I'm sure you can find other examples of services that integrated with Google Reader. I didn't include all the third-party apps and services that used the unofficial Google Reader API. As you can see, Reader was an important part of the Google ecosystem and Google did promote the service in many ways.