Orks reliable?

Orks reliability.  Most who play orks would say otherwise.  Orks are predictably unreliable, and that is why most players choose Orks in the first place.  Most players will compensate for that weakness in creating a list that will be solid.  In other words, an intelligent general will often hide the flaw of his army in order and play to his strengths.  It is clich'e but, it is another facet of 40k by now.

So, how do ork players hide the nature of the army, and use it to their advantage.  Well, most opponents will assume they can expect a few basic things about orks.  1.) They are going to utilize speed to close in and get into combat quickly.  2.) They will use a lot of boys.  3.) That they will be grouped together to avoid template weapons. 4.) That no matter what, the orks will try to get into combat where they excel. and 5.) They are unpredictable.
While this may be true to a certain extent, it is by no means the only way to play orks.  Since your opponent knows that your Orks are unpredictable, use it to your advantage.  Switch your lists up, try something new.  Don't be afraid to try a shooty ork army.  (Especially if facing the Tyranids.)  The basic shoota gets 2 shots, so if you have 2 units of 30 boys in range, with 3 big shootas in each squad, that means you are going to roll 126 dice.  Assuming you are concentrating firepower at a unit of 10 marines, 42 of those dice will hit, causing 14 wounds.  Now Marines will save two-thirds of that, so approximately 4-5 marines will fall.  (Utilizing math-hammer.) What about 2 rounds of shooting.  Assuming that the Marine will stay in range. But, if they don't that is why shootas are great weapons. (Assault 2)  You can just as easily move into range, and fire away.  If they tricky marine player was using the squad as bait, to lure you into range of a big template or massed firepower.  You always have the option to go to ground.
The bottom line is, the orks are unpredictable to a points, and to utilize that, don't give your opponents what they expect.  Create lists that are "different" and "unusual".  (Which is why I always liked the shooty ork list.)