This is a bad idea.
Sometimes, there's bad content
If you have a way to like a post, you need to have an equivalent way to "unlike" a post. That's the only way the community can truly have input on whether or not content is valuable. People post bad info here all the time. Many times, it's based off personal opinion and not facts. Which is fine, as long as the post is clear that it's an opinion.
Not clear how it will be used
I think there are many ways that having a like/dislike option associated with a post can be valuable. But today, there's no plan mentioned for how this will be used.
Will there be some sort of "award" for the most valuable content in a forum?
Will this be used as criteria for selecting forum mods/ambassadors?
Will there be a way to filter to only see content of a certain level?
Instead, I think it'll be used by people who think these things matter on the internet (the same ones that feel their post count actually matters), and they will be recruiting all of their friends to form a "mutual admiration society" where they all just "Like" each others posts, no matter what the content. I would consider that an abuse of the system. FT would need to have clear policies in place for abuses like this. It will require additional mod time to perform these sorts of investigations.
If you don't have a clear plan in place for how it will be used/abused, then you shouldn't implement it.
There's no clear benefit to FT
There's no mention in this proposal of why FT thinks it is needed, or what value they believe it brings to FT.
Potential for abuse
In addition to the abuse described above, an admin for another forum has posted real-life experience of how it can be abused:
http://www.flyertalk.com/forum/23873665-post111.html
Other options
If you're going to implement some variant of it, I would be in favor of the solution proposed here -
http://www.flyertalk.com/forum/23873665-post111.html. I think there should be additional discussion on what the categories for the voting options would be, but otherwise I agree with all of the advantages/disadvantages described here.
It also NEEDS to be anonymous, or you will have drama.
Every forum that has added/changed this sort of functionality after going without it for years has experienced pain. I encourage you to look at the history of some big boards that have done this, and see what you can learn from their growing pains.
I also "dislike" the idea of having a link to every thread I've "liked"
http://www.flyertalk.com/forum/talkb...-profiles.html.