Security is useless because once you get the Skeleton Key it becomes a useless skill in major. Merchantile is useless because it increases so painfully slow without training. But putting a skill in major isn't everything. The first skill I mastered was Armorer and its not even one of my majors. But yes you can screw up a character by choosing the wrong skills and theres virtually no option for hybrids. My current character is the only working hybrid I know of. Check my sig if you want to know what it is.

heh.
Jumping wherever i go is an old habit from Morrowind.In Morrowind you would actualy move faster while jumping.I carryed my habit in Oblivion,and i became a master of Acrobatics,developing it as a minor

Ahh Morrowind,the memories........

That's not true.
The game is so ''slack''t that you can make some really wicked hybrids even if you don't intend to.
I intended to play the game as a stealth char.Somewhere in later levels i developed in a quite a figher,and i was the master of Illusion even though i developed it as a minor.I also boosted my Inteligence with Alchemy,so i had enough magicka for some good spells too.I got intrested in developing a little Mysticism and voila,i'm a master.

About Merchatile:I can't confirm this because i'm not a master,but i heard that you can ''invest'' your money in shops,so that they can have more money.