I know I have posted this before, but it seems it was long enough ago that it is no longer available.
Basically, there are two reasons for minions. One is to let the players feel awesome as they mow through 1258 Kobolds at level 10 and save the town. This is completely valid for a DM to use, because sometimes you just want your party to feel awesome. Also, if you need your players to level, this is a flood of XP.
Then there is the way minions are described in the book. The orc that zigs when he should have zagged and gets an arrow in the face, the hobgoblin that steps in a gofer hole as he tries to block, or the drow who happens to stand up at exactly the wrong time and gets reduced to ash.
The first kind of minon, the players can even know they are minions and target them appropriately. They are one hit kills, and do small flat damage. A miss never damages them, and they have no non-minion equivalent.
But the second kind should not be distinguishable from an actual non-minion monster. They can be used to make it look like overwhelming odds, adding tension to the game, and can't be singled out in a crowd.
For this, I use what I call minionized monsters. I take a standard monster (non elite, solo, or swarm) that I will be using in combat, and I give it vulnerability equal to it's bloodied value to attacks that hit, and make it appear bloodied at 1/4 HP instead of at 1/2 HP.
This way, if it is hit twice, it will go down. If a striker does enough damage to it go down. But if it gets missed by a fireball, it still takes damage and may or may not go down depending on if it has taken enough damage from other sources.
I find that the minionized monsters, at 1/4 XP value, are much more XP appropriate per challenge level for standard encounters (a.k.a. encounters where I am not going out of my way to level the players sooner.)
I find that my players take the combat more seriously when they can't tell which monsters are going to be around for how long, and they seem (with the exception of my <b>Rules Justicar</b>, who disapproves of house-rules he has not invented) to enjoy and revel in victory more.
Of course, I also have house-ruled out Essentials and all the changes made to accommodate the new Magic Missile, so YRMV.