A Tome of Mastery should act in the same way as a necromancy table. You can also spot a necromancer a mile away from the fact that everything around him is dead >.>
However I'd be careful about the idea of the table causing damage to plantlife, both grass, crops and trees, as you open up a lot of griefing options. (Worse so would be the Tome causing similar effects)
Perhaps the death of the necromancer (or maybe even just his extended absence), would start a timer for each monster, a Minecraftian day for death (and a Minecraftian week for absence) at the end of which, the monster in question would become hostile to all; a further day and the monster would disintegrate.
To restore control, the necromancer would have to return to within x distance of the monster and read from the Tome of Mastery, aka the Silk-Bound Tome, aka the 'spider tome'. The distance should be fairly large, so that one would not have to perform the ritual several times for the siege of a single castle, or for the defence of a single castle.
Reading from the tome whilst pointing directly at a hostile summoned mob would bring that mob under your control - whether it was you who summoned it or not. This counts as two uses against the tome. This also takes some time, during which you and the mob are immobilised; either may be killed, but you may release the RMB and run for the hills if you wish. You may not seize control if the controlling necromancer holding the Tome of Mastery is within x/2 distance (or is that too much to code... just worried about constantly swapping monster control between two necromancers until one tome disintegrates).
So the process would be something along the lines of...
Target, RMB: Begin reading from the tome.
Target is immobilised, begin checks.
Check for master, check for distance to master.
Check if master is holding Tome of Mastery.
Success: Finish reading, change master id.
If master distance is <x/2 and the master is holding the Tome of Mastery, you fail and the monster turns on you.
Something to note here would be that the tome must be the active item, not just in the inventory. This would mean that to be a proper necromancer would be a full-time occupation in the larger battles, not just something to keep the enemy busy whilst you run around shooting arrows like a lunatic.
It also solves the problem of losing a skeleton in a cave somewhere. If you die, the link is severed and they try to kill anything nearby. If they don't die then, they disintegrate a little later.
On second thought, I don't like the idea of just being absence would trigger control loss. It would prevent you from garrisoning your castle and going mining.
Tome of Mastery should be one of, if not the highest level tome, requiring a significant amount of materials to make as it is the 3rd or 4th iteration of tome. This justifies it being a tome of 'Mastery' in the first place, as it contains the knowledge and power of all the preceding tomes, and has the same materials 'of power'.
Any other uses for spiders? Would be kinda nice for the spider based summons to be done with a silk-bound Spider Tome, but with only one spider summon, it's a bit pointless, especially when that happens to be the rarest summon ever.
Same as a spider I guess, just with the "summoned spider" skin...
Think of the guy who built a fully functional 16-bit ALU out of redstone. It's complicated to no end. The possibilities are there. Does this affect the complexity of how you play? No, it does not.
Now, here's an idea for a very high level summon.
The spider ballista. It's basically an oversized crossbow mounted on the back of a summoned spider. (Retextured to look summoned; perhaps made from skeleton bones?)
This requires a skeleton's bow, acquired by sacrificing a skeleton riding a spider. Now these only spawn once in a blue moon, so balance is solved.
Spider ballista moves slightly slower than normal spiders and doesn't jump nearly as often. It does however inherit spider movement abilities (should we ever have spiders able to climb up walls and onto ceilings). It fires the crossbow with a much higher velocity, flatter arc, but far less often than a skeleton, and for a bit more damage - perhaps 4? It cannot shoot downwards, and thus has a minimum range (though the spider can still bite, though for a lot less damage than usual).
Red representing where the arrow trajectory may be, and green where it cannot be. The arrow and chest represent the firing point and ballista respectively. As you can see, a player can hide under the arc and kill the spider. (Not to scale horizontally)