I've always wondered how effective the disintegrate perk was in destruction. Anyone know?
Woo! Came just for this

The Disintegrate perk can be absolutely invaluable.
See that group of level 40+ mages that always gives everyone a hard time, even on Adept? Well, they're surrounded by undead, and if you kill one, his buddy will simply raise him right back. With groups of powerful mages, you essentially have to fight them twice. But with the Disintegrate perk, you leave no chance for that.
On top of that, it works when enemies are at
low health. That means that you can potentially get a one-hit-kill on someone who would otherwise take a few more shots. If you brought down an ancient dragon's health to maybe ten or twenty percent (and, say, there's a freakin' dragon priest nearby), you can switch to a simple spell like Lightningbolt or Sparks to get the job done.
I think it's also a bit of under appreciation when people take Block perks to compliment One Handed but ignore the dual wielding branch. For just three perks, you can significantly change combat on the fly and become offensive or defensive whenever you need to be.
The specific weapon perks are also under appreciated, as far as I've seen. Of them, the axe perks are the best--almost everything bleeds, and bleeding damage stacks. That means it's already good enough with a battleaxe or to give your warrior defensive DoT if they're using a shield, but two axes can make quick work of anything, even ancient dragons.
The right side of the Enchanting tree isn't popular, either. Just two perks and you can now use enchanted weapons with a lot more lenience. Definitely worth the investment, IMO.
Obviously, very few people like the Cushioned perk under Heavy Armor. So few, in fact, that most people just use the Steed stone to save them the trouble of getting that perk just to have Conditioning (and I don't blame them).
In Smithing, Advanced Armors is under appreciated. People don't like that you don't get weapons or shields with it and that it comes with a heavy armor set. What people don't consider is that Scale armor is cheap to make, valuable to sell, and a whole lot easier to acquire (material-wise) than the components for Elven armor. Also, no one other than myself (that I know of) is fond of creating a heavy armor warrior who uses the light side of the Smithing tree. You get great steel plate armor and lightweight weapons--while they may not be as damaging, that means more weapon sets (for weapon masters/collectors/enchanters) for different encounters and faster-drawing bows.
That's all I'm going to go over for now (don't even get me started on Lockpicking), but a lot of the game's most interesting (and useful) perks go unappreciated.