YOU'LL HAVE SO MUCH FURNITURE
GRATUITOUS AMOUNTS OF FURNITURE
YOU'LL BE MAKING FURNITURE SO FAST THAT MOTHER NATURE WILL BE LIKE "sloooooooooow dooooown" AND YOU'LL BE LIKE "[censored] YOU!" AND YOU'LL KICK HER IN THE FACE WITH YOUR LEGS
FURNITURE LEGS
But anyways, if Rhekarid is going to able to talk about traps, I might as well re-mention the permanency spell I thought of a million and one threads ago (Rhekarid has already well integrated it into his magic system, if I recall).
Basically, it's like this. There is a spell (Mysticism) that can be cast to make a targeted enchantment (on a door, for instance), circle (a magical circle that is selected during spell making, as part of the ranges for the spell. There would be aura, circle, wall, cone, target, touch, and self), or aura (if they would allow auras to be cast not only on yourself but on other things as well, to make the Flaming Cup of Always Burning Coffee, for instance). This will, as the self explanatory name says, make the target permanent. If it is a trap that does an offensive effect, only enemies can trigger it. Friendly effects can be set to trigger when stepped on, or trigger when used (No one liked accidentally stepping into the light shaft in Ocarina of Time and then having to run all the way back to get the heart piece).
Now, this would not be some free thing, however. It would cost a soul gem, basically to bind the magic and use the power of the soul to keep the spell fueled with magic. These permanent spells could be used to very powerful extent. Rhekarid's example was a fine one; a mage using a recall circle to hide his true lair. Other tricks could include making a recall spell on a chest permanent, and then putting mark on another one, allowing one to instantly teleport one's goods and wares between both chests. Obvious uses include putting a fire spell on a circle so that thieves will burn instantly upon touching it, but other uses are more crafty, such as enchanting a circle to summon a Dremora to drive them off, which will then ensure their death, even after they step off of the circle. Flaming walls of fire could sit in a dungeon for eternity, with the only way of passing to either sate the floor with water (which won't hold off the magical flames for long), or dispel the damned thing altogether.
Friendlier uses include healing circles, or ones that would cure ailments. One could use a circle to ward off magic, as contradictory as that sounds, such that purely magical beings could not pass. Detect magic circles or auras could also provide useful to one who wishes to keep an eye out, allowing one's front door lamp to keep vigil. There is always the ever popular option of locking a door permanently (with a lock spell, of course), for double security duty.
One's permanency costs are dependent upon the power of the spell, the kind of spell, the kind of type (circle, wall, aura, or enchantment), and sometimes smaller things, like the material of door one is enchanting. Other factors (like if one was doing this in Oblivion) can raise or lower costs as well. Skill in the spell schools used in the enchantment are also factors. Souls increases uses (a fire circle bound with a rat's soul could burn someone for around 5 seconds. A circle bound with Vivec's soul could burn someone for eons). Souls, skill, and other factors also increase the magical resistance of the enchantment, although this can be edited when making the spell permanent, if one wishes to reduce or remove any spell resistance as part of the overall plan.
Such enchantments would also have much customization to them. One could direct a circle to direct its power inwards or outwards. They could place it on the wall, on the floor, and even on an object (but that causes limitations with materials. One could, unfortunately, not have shovel spiked with 12 foot wide and tall walls of lightning. It could be spiked with lightning, but to a much weaker extent). Such customization allows one to think very cleverly about applications. A circle of magic binding could hold a magical being inside of it, whilst simultaneously burning it with flames. Other devious applications include multiple cascading effects; a gigantic circle with suppress magic (inward) is large enough to encompass a room. There is another circle, slightly offset, and much smaller, on the other side of the circle. On each wall, on the floor there is a wall of flame spanning the width of the room. When the unsuspecting adventurer steps on the small circle, which is a circle set to dispel magic when set off, it will dispel the circle (because of the aforementioned ability to remove resistances if one so desires). The large circle is dispelled, releasing its ability to hold off the wall of fire, which now splits the room with a veil of wreathing flame.
Then again, that's only if we wish to keep circles and other enchantments purely magical in nature, rather than allowing them to be connected as triggers for other enchantments. That trap could just as easily be a circle that, when stepped on, activates the walls of force. However, my real point is that Bethesda could make all the spells rather easy to trigger with the enchantments, yet players could make extremely massive and elaborate traps and utilities out of them interconnecting, simply because of the spells and how they work together and affect one another.