github
On the GitHub contact page, I see the following message:
If you use 140 characters or fewer, we'll give you a gold star.
I sent a message that contained 139 characters and I got a gold star.
What does this mean? Is it just for fun or does it have any usage?
It's for you to keep track of gists that have made you smile or caught you off guard and you want to have a list of them stored at Github.
It is just like a bookmark system. You mark a star on a gist you find interesting or like and then you can find them at a glance under your account at starred gists.
The link to your starred gists will be there for your account, but if you have nothing, it will simply prompt you to create a new gist. One that you may star yourself.
The big difference between watching and starring a project comes down to notifications.
If you are watching a repository, you will receive notifications for all discussions — project issues, pull requests, comments on commits and any other comments. If you’re not watching a repo you’ll just receive notification for the discussions you participate in.
On the other hand, if you star a repository, you basically want to show your appreciation as well as keep track of repositories that you find interesting without it spamming your timeline.
This is clearly stated here in the Github blog post,
A quick note: activity from starred repositories will not show up in your dashboard feed.
The other main thing worth noting is that any repositories you were previously watching can now be found on your stars page. If you want to go back to watching them, you’ll need to change them over yourself. There’s also a new auto-watch feature; when you’re given push access to a repository GitHub automatically adds it to your watch list.
You can see a list of your starred repos at github.com/stars.
And popular starred repos at github.com/popular/starred
Best Answer
It's just for fun. It's much the same as if you vote my answer up 100 times and I get a badge. If you could do that, I'll let you know if that or the gold star gives more virtual satisfaction.
The advantage is more for GitHub, it's a very clever way of reducing support requests down to the absolute minimum text. If the same were applied to answers on this site, I'd not have added the attempt at humour which adds nothing to my answer.