You do have a valid point. But it still not be so easy.No-one is forcing me,but we all get tempted.And whether i use it or not,do you not think it more entertaing/realistic,or whatever to think a wolf or some other creature,that uses smell aswell as sight to detect you.Do you not think it's reasonable to expect AI to cast detect spells.Invisiblity should not be fullproof,you still give a smell off and sound.It shouldn't be ( in all cases ) well i'm invisible,nothing can touch me.It just doesn't go down well with me at all. The spell/how it's used/how the AI react to it does need looking at.
Well, its an illusion spell so it doesnt actually make me invisible, its not alteration.
What it does is that it stops the person affected by the spell realising they see you, their senses just ignore you, erase you, like the blind spot in your real life vision.
So I dont think creatures should hear or smell me as those senses would also be affected by the spell.
But it would be great if a higher level enemy NPC has a detect life spell or ability, and then cast an area effect dispel.
In Morrowind the invisibility spell could not be used when in line of sight of an NPC, it wouldnt work, they could still see you.
This was because its an illusion, and its of course not possible to fool someone into not seeing you when they are looking right at you.
I dont remember if this was the case in Oblivion, but I would like it in Skyrim.
Coupled with that you cant open doors, pickpocket, take any item without it dispelling would provide a good downside to the usefullness of the spell.
You wouldnt be able to pick up an item in a crowded room and dissapear, because enemies have you in their line of sight.