I agree with 5chdn (but I talked too much for a comment).
Having the most specific tags for things is always good - especially if there is content to fill them.
- shapeshift is a good tag as there are quite a few questions that are specifically about Shapeshift and not much else.
- A question should not be tagged Shapeshift if it merely mentions that service but the question really has to do with, say, confirmations.
- When creating a new tag, the community member should do their best to retroactively tag related posts as well. IMO, no tag should have less than ~5 questions. This helps with discovery (more on that later).
- In this discussion, metamask comes up as an example. At this point, I don't know if there is enough content for metamask to be a worthwhile tag. However, in 6 months there absolutely may be.
The key here is that the question is a question where the main issues / question / content pertains specifically to that product or service.
Yes: "How does etherscan put names on addresses?" is a question specifically about etherscan. Having an etherscan tag would be worthwhile here.
Maybe: "How do I view my account balance using etherscan?" is not as deserving as it really pertains to any blockchain explorer, not just etherscan. It could be tagged etherscan and explorer or just explorers. (IMO, it doesn't really hurt to have more tags as long as they aren't off-topic). The question would also be helped by being edited to refer to all blockchain explorers.
No: "Why did my transaction fail? ... I looked on etherscan and it says Out of Gas..." is really not deserving of the etherscan tag as etherscan is simply mentioned while the issue has to do with transactions, not the blockchain explorer.
"A tag is a word or phrase that describes the topic of the question. Tags are a means of connecting experts with questions they will be able to answer by sorting questions into specific, well-defined categories."
First, developers of many of the products and services are active on StackExchange, so having a tag that they can specifically go to to answer questions could be super helpful in that sense.
Secondly, I don't think that description covers the full use case of tags in Ethereum StackExchange's case. While this is absolutely true for larger communities (ie: StackOverflow), at this point tags also help immensely with discovery and learning. Maybe I'm the only one that ever views related questions in a tag, but I learn heaps by reading and examining discussions on threads - even threads I have no intention of being able to answer.
With such a new technology, there aren't a ton of blogs or discussions online about a lot of the things that are happening right now. If I want to learn about CSS, I have tutorials, blogs, books, lynda.com, and so much more. If I want to learn more about Solidity, I have (1) the github repo / readme (1b) MAYBE one Ethereum blog post (2) a couple reddit threads and (3) StackExchange. The Etheruem StackExchange is especially helpful in learning how the specifics of a technology and how real people are using it.