Google Friend Connect will be replaced by Google+ pages. It will still be available until March 1, 2012 for non-Blogger sites, while the Blogger feature will continue to work for a few more months. Google Wave will become read-only on January 31 and it will be closed 3 months later. The Gears-based offline mode will no longer work in Google Calendar and Gmail starting from next month, so if you're still using an old version of Firefox or Internet Explorer for this feature, you'll have to switch to Chrome. Bookmarks Lists will continue to work until December 19, but I'm sure that not many people will miss it.
Knol is a project that attracted experts who wrote a lot of interesting articles, but it wasn't successful enough to make a difference. After all, Knol was a niche service and Google's goal is to "focus on products that can benefit the most people and solve the most important problems". Google informs that "Knol will work as usual until April 30, 2012, and you can download your knols to a file and/or migrate them to WordPress.com. From May 1 through October 1, 2012, knols will no longer be viewable, but can be downloaded and exported. After that time, Knol content will no longer be accessible." Why not preserve the content? Some Google Answers pages are still useful after so many years.
It's interesting that all these projects, except for the Gears plugin and the timeline option, had a social component. Now that Google+ is Google's social hub, it makes sense to replace these projects with Google+ features.