It's way too easy to level pickpocketing. In Thieves guild you can pickpocket everyone, and even if you get caught nobody will do anything about it. You just have to try to pickpocket everyone, leave the room and do it again. By the time you took everything you could from them, you will already have pickpocket at 35-40, and if you perked it, you will have no issues to pickpocket items who worth up to 300-400 gold from people outside.
You will get + 1 level (If you have thief stone) for every item who worth more than 150 gold (More valuable items required as you level), and as you level, you will have 90% chance to pickpocket any item. Most of the people will have enchanted rings and necklaces who worth up to 800 gold, and leveling is just way too fast. Also, being member of the Thieves guild, if you get caught you can bribe guards for miserable amounts like 12 or 30 gold. Ofcourse you can sell all those goods in Thieves guild, and basically one run = + 20 pickpocket skill (Between 40-70) and more than 3000 gold value of items you stole. Also, you will lose max 200 gold for bribes and there is also gold included from pickpocketing people. Basically you will cover up your bribes with gold you took from the pockets and have clean profit from other items + your pickpocketing skill goes very high. In one hour, you can get 100.

That's beyond silly, and while I'm aware there are other skills like Illusion or Sneaking who can be capped very fast by abusing game mechanics, Pickpocket also provides you with very good items and lots of gold as you level it with no investment at all.
As Smithing got fixed, I think Pickpocket should have the same treatment.
I guess nobody is forcing us to use Pickpocket that way and level it up fast, but nobody forced us to use smithing as well, and yet it got fixed.
I know many people know this thing about pickpocketing, but it should really be changed, since you can use perks of it for a huge advantage (Taking whole armor and weapon from some bosses).

The whole pickpocketing mechanics should be changed, perhaps in some kind of a minigame like lockpicking, when you can take items from someones inventory, and it's difficulty is determined by the value or size of particular item. It would be way more fun than this.
If not, at least it should be more difficult to pickpocket, and fines for pickpocketing should be scaled by the item value (Exmpl. Necklace worth 160 gold should be 48, while ring worth 500 should be fined for 150 gold).
And let's not forget how you can easily pickpocket money from your trainers for other skills, paying 2000 gold for one-handed and then pickpocketing it back with 90% chance of success.