The only thing that worries me about Dragon Age styled toggles is how overpowered Arcane Warrior was, more so because of how many toggles a Mage with Arcane Warrior spec could toss out and that they could become literally stronger then a number of the actual bosses... by themselves. Also I think Magicka regeneration should be slowed rather then harsh caps put in place, some caps would be fine but Dragon Age went a little far with it's caps (then again it allowed a lot of toggle spells). I think there should either by a cap number of toggles you can have or there should be a cap % of Magicka that you can sacrifice to have toggles.

That problem is somewhat limited in Oblivion/Skyrim due to how the magnitudes of the buffs actually depend on your magic skill level such that a warrior would either svck at magic such that sacrificing all of his magicka for low level buffs wouldn't really do much for him OR he would have to spend a LOT of time leveling both his melee skills and his spell casting spells that it would probably be too much hastle (especially if magic skill ups came based on the amount of time a spell is sustained rather than per cast). Conversely, a mage practicing his melee skills would also have a very slow progression to become overpowered as a buffed up warrior.

This problem is also somewhat addressed with my suggestion of buffs falling off if you run out of magicka. Given a system where magicka regen is reduced with buffs such that eventually (let's say, 2-4 buffs depending on how good the buffs are) you get negative regen rates (ie. your mana is being drained), you wouldn't be able to sustain the buffs for very long since you'd quickly run out of magicka and lose the buffs. This is especially true for warrior characters who have low magicka pools (low intellect) and much slower base regen (low wisdom).

Bump for less annoying spell casting. I'm still doing my replay through Oblivion and it's ultra annoying to have to keep refreshing Feather, Detect Life, Light, and Armour. There's also the issue of having to spam your cheapest Alteration/Illusion/Mysticism/Restoration/Conjuration spells to keep leveling those skills up. In fact, having skill ups for these schools be based on sustained time rather than per cast would put mage leveling more in line with melee/archer specialists who can only really level if an enemy is around (ie. not in the safety of their home).

Then why have it a spell at all?

Sustained spells would work well for some things, as mentioned feather or night eye, and other duration spells it might be negative for, depending on tje player.
So it would be nice to have the option to make it sustained, or just cast it for a duration. Everyone wins.

So I could cast feather "forever" (with reduced regen), or for 30 seconds to walk from one vendor to the other. I could cast shield for the whole dungeon, or just for 1 fight. I could cast water walking for my whole lake voyage, or just for 15 seconds to cross that river. And since we know we can cast a fire spell in different ways, I expect we can cast duration buffs in different ways. This is one such way we could have different effects.

Just saying, I wouldn't like it exactly like Dragon Age: Origins because of how overpowered it made Arcane Warrior, I am fine with toggles, as long as they balance/scale. In fact I'd rather racial abilities be toggles rather then greater powers... it makes no sense that some races can only do things once a day, like how an Orc can only Berserk once a day.... or how a Red Guard only gets his Adrenaline Rush, once a day... Racial Toggles of course wouldn't draw on magicka or increase skills, They'd just have negative effects that offset them. Say Breton's Dragon skin that gives 50% Shield would stunt magicka and damage 1 magicka a second until at 0 it auto cancels. Berserk and Adrenaline Rush would have change just because those names are for short term things but they could have similar changes of sorts.

But as for spells, Feather, Detect Life, Night Eye and a few others make a lot of sense. What wouldn't make sense are more powerful spells like reflect damage or absorb spell, unless they were to a very low effect, like 5%/5 points. Again, I still think there should also be a total limit on toggles (not including the racial toggles that I suggested above), perhaps make it so you can have an active spell toggle for every 20 Intelligence that you have.

Just saw another thread with a similar suggestion except that, instead of sustaining the spell, you could charge it up during the initial cast to make it last longer. This type of change, that is longer buff spells, seems to be something on the back of a few people's minds.