One of the few articles I was very interested about this month, Game Transparency is all about how and if you should dispense mechanical information to the players, as well as a few techniques on doing so.
I like to use a combination of explaining stuff in the game narrative while coupling it with mechanical terms. I might describe the effect of a scorching burst barely affecting a hell hound, but I'll also point out that the monster seems to be resistant to fire to ensure that everyone is on the same page. I could have them roll for it, I suppose, but in the end someone is likely going to figure it out anyway and I find that its just easier to keep things rolling.
When it comes to the bloodied condition and minions, I reveal these things straight away. I used to demand a skill check to notice this, but I've had players burn encounters and dailies on minions, and thats pretty lame. Call it "badrongfun" if you want, it doesnt add anything to the overall challenge of the game, especially if the characters dont have any cues to work on (and if you are providing cues, chances are they are going to figure it out anyway).
For players with high skill bonuses, I like to reveal the easy DC lore right away to set a foundation for what they know. If they want to know more they can give me a check or just take 10, something that I feel lets them play it safe or take a risk. I'd played around with rolling Perception and/or Insight checks to see if they noticed stuff like recharging abilities or regeneration, but in the end I think its too much rolling for too little payoff.
My philosophy is that I want the game to keep moving and avoid having players arguing over interpretations and tactics. Its not a big deal to reveal resistances, minions, and recharges. At best you are dragging combat out for a bit longer than it probably should be, and in all actuality I find that if I tell them that the dragon has recharged its breath weapon that its a surefire method for getting them freaked out.