@HungThir: The Manager does round robin for as long as you have the material, but once you're out of material the job allocation will start at the top, so you produce one cloth, one pant order is generated, and there's nothing for the others. Once you've produced a second piece of cloth the allocation starts at the top, i.e. pants.
The manager orders can PRODUCE different sizes, but it cannot base the production on the same size, so if you have 11 ogre sized pants from the last siege, the check will say that you have more than 10 pants, so your humies won't get any new ones.
Once I have 10 non masterworks pants production stops producing pants. There will be a short production spurt after you've sold off the garbage, typically consisting of 1 masterwork and 9 sub par quality ones.
Workshops: Exactly. The moronic manager will split the stone crafting jobs over all of the stone crafting, wood crafting, and bone crafting craftdwarf shops, resulting in all crafting grinding to a halt once a crafter gets a mood, gets to sleep, or goes on a socialization/prayer bender, because his type of job sits at the top of the list in all the workshops.
I strongly disagree about the quality of the Manager. It's got a number of elements for a powerful system, so the potential is there, but there are too many parts missing for it to actually work decently. Many of the problems lie in the input criteria (it doesn't know how to figure out if you have any shearable animals, for instance, resulting in a steady stream of cancellation reports if you try to use it), but you also have production deficiencies (want your still to top up your stocks of Swamp Whiskey? You're out of luck, unless you think producing random types of (plant based) booze until you've happened to produce enough Swamp Whiskey is rational). There is no support at all for time of year (fruit ripens during the summer, so you might want to cut down on some jobs and ramp up on others, for instance). Size, wear, quality: all missing. There's also no support for dedicating workshops to particular tasks, although you can work around it to some extent with skill limits, as mentioned. However, you'd want your web processing loom down by the cavern to handle web collection and processing, not the "ordinary" ones, for instance, and I want my Farmer's Workshop by the pasture to handle shearing/spinning, not the one down in the workshop area. Note that DF itself has the functionality for ordering the production of e.g. a particular type of booze, but neither the UI nor the Manager supports it. I've mentioned the lopsided handling of production orders on supply shortages: there's a need to be able to group production so round robin production is performed within the group even when the supply dries up: when supplies become available again production should continue where it was broken off. There's a need for multiple use input to be split into different production chains rather than have the production being random based on in which order dorfs happen to take the jobs (in particular if you're short of dorfs, so they have multiple hats). Try to use the Manager to split Pig Tails into cloth, booze, and food, for instance.