Recs.
Updated
SpecsUpdate
Pros
Pro Feels and acts like a "social network for coders"
GitHub sometimes acts also as a social network for coders. It has different features that allow users to follow or star their favorite projects. The user's account page is like a Facebook wall with projects, pull requests, forks, pushes and merges all displayed. The main dashboard after logging in also displays news from followed developers or projects.
Pro GitHub makes it easy to find open source projects
GitHub is the largest host in the world for open source projects. Developers from all over the world fork and work on countless projects hoset on it. For this, GitHub has some excellent features that help both new and experienced devs to find and commit to open source projects of any kind.
Pro Supports Two-Factor authentication
GitHub has added another layer of security to their user accounts. This layer comes in the form of Two-Factor authentication. After it's enabled, GitHub delivers an authentication code by SMS, or by a free application for smartphones. After two-factor authentication is enabled, the authentication code is sent to the account owner's phone any time someone attempts to sign into their GitHub account. This means that only someone who has both the password and authentication code can sign into the account.
Pro Large community
GitHub is the largest code host on the planet with over 21.4 million hosted repositories and many users. It's unarguably the largest VCS used by developers worldwide and as such, it has a vibrant community that follows it resulting in many guides and tutorials for new users. Even experienced developers can always find an answer to any question they may have.
Pro Nice and usable UI
GitHub's UI is clean and intuitive. Each view is designed to not fill the screen with useless information.
For example, the repository view displays only the most crucial data about that repo - on the top it displays the number of commits, branches, releases and contributors. When clicked, each of them will take the user to a page that displays more detailed information.
Cons
Con Proprietary
The whole source code is not available to users in Free/Libre/Open license.
Con It can be difficult to migrate away from due to it's central position in the ecosystem
Due to the fact that it's proprietary and that many external services integrate only with GitHub, it's becoming harder and harder to migrate a project away from it.
That will be a big issue the day the company will make controversial choices (like SourceForge)
Con Using it encourages other tools to integrate only with GitHub, leading to a monopoly
Con GitHub is known for deleting files they don't like despite not breaking the sites TOS
GitHub has in the past removed content from their site that is not breaking their TOS. Examples such as the E Plus Equality project as well as the operation disrespectful nod repository have been removed despite not breaking any site rules and appear to have been done out of employee distaste.
Considering the amount of content allowed on the site that is full of rude or vulgar humor, to single out these projects for removal shows employee politics and agendas take the front seat over an open and tolerant environment. Which is quite contradictory to open source ideals.