This feature would explode activity on my site, especially within our art threads, where a long, drawn out comment isn't expected, like with our fiction. Being able to "Like" your favorite piece of artwork is super easy and quick, and would eliminate all the "Beautiful!!" and "Awesome work" kinds of comments we get in our art groups.
We also would need a way to manage our likes. As it is now, we cannot delete anything from our "My Likes" pages which is silly. If you're going to have a page for your accumulation of likes to begin with, then you should provide a way to delete ones you don't want or need anymore. What I liked three months ago may be ho-hum today.
And I know it's not on the Product Roadmap, but it would boost activity on a lot of networks, not just mine.