Mid laners are definitely not entitled to blue buff. But, as a jungler, we need to weigh whether or not the buff is better used by us or by the mid laner (and very rarely the support).
Some junglers need the blue buff for the entire game, some only need it for first clear. If midlane is ahead, and you want them to carry the game (and you do, that's part of what jungling is: getting your lanes ahead so that they can succeed and bring your team closer to victory) then you should probably give them the buff. If your mid is feeding and they're 0/4 by the time second blue is up, you absolutely do not give it to them, that's called stupidity.
It's all about judgement calls. But every time the buff is up, you need to ask yourself: Who is the most beneficial recipient of this buff? If it's me, then I'll take it. But if I don't really need it and someone else would do better with the mana regen and CDR, then you'd best give it away, because you're wasting resources!