There seems to be an increasing problem lately that newer users leave off the most obvious tag - the tag for the language/platform they are using!
For example, see this question: Oracle - how to remove white spaces? The title clearly states that the question involves Oracle, yet it is only tagged with query and whitespace. (This is actually very common with SQL or database related questions.)
I used to leave a comment explaining this issue every time it happened, but it has been happening so much lately that I mostly stopped doing that.
It is more of an issue than you would think, since without a common tag such as c#, few people will see it because of the interesting tags list, and often, these questions go like this for quite a while before somebody retags them.
I think SO needs some sort of notice by the tag input box explaining this. Is this a good idea? Do you think it would help fix the problem? Is there a better way to do it?