I've done that a few times, and always felt anxiety before hitting "submit". So far I've had mostly good reactions to it, but I've also had it ignored and the ticket silently closed.

Probably depends on the person. I would kinda mind that.

Doesn't feel personal enough. It would be helpful to be able to express what you like about a piece of software.

That's what I use stars for anyway.

Let me pile on btw: great tool!

I'd be happy to use a first-party system designed for simply saying why I like something. However I'm not willing to create a Twitter account just so I can thank someone when we've never met (and likely never will), and are likely never to speak to each other again. Same deal with signing into other services through GitHub (like gitter), that might start sending me emails (when signing in via GitHub, the service gets your email address; so far as I know, gitter doesn't use it for anything, but other services might).

Unclear, I think. I tend to use GitHub stars as bookmarks, which implies interest but not necessarily hearty approval.

I don't think you can generalize here; it's like Twitter, where some people use Likes to remember all-time favourites and some people use them as an "I've read this" checkbox.

Besides the thing sibling commenters mentioned about GitHub Stars acting like bookmarks, I also feel that GitHub Stars are more intended to be used to indicate interest in the source code itself—which is a bit different from indicating interest in the product you get by compiling said source code.

I might Star e.g. Postgres (yeah, I know, not their official repo) because someone told me that it's an example of good, elegant code, and I would like to study it. But that doesn't mean that I'm a Postgres user, let alone an adoring fan. I'm starring the code.