[Radek]

1. The skills. Nobody has made the list so far. Here is my personal experience:
(a) As Bsftcs has said, the weapon skills improve by practicizing them. But, usually, they improve only if you really use them. The Sword skill will improve only if you fight with a sword, and so on.
(b) Magic users improve all their "natural" magic shools (the ...craft skills) but they do not improve the rest of magic schools.
(c) Mages, Warlocks, and Zenmasters improve the Sorcery skill by casting spells.
(d) Thief-like characters (thiefs, barbarians, ninjas, assassins, and bards) improve the Lockpicking skill by picking locks and the Pickpocket skill by stealing.
(e) The rest of skills does not(?) improve by practicizing and you must train them by investing skill points or by training in guilds.

2. The inborn traits. IMO, the Quick Learner and the Mana Seed are the only valuable inborn traits. The rest of inborn traits represents either no advantage or only a temporary advantage. Beware of pixies! The Dodge trait looks very interestingly but it causes pixies to dodge their own spells! It's a very annoying bug, which can make you ready for a madhouse at higher character levels. Pixies are almost unable to cast defensive spells on themselves.
Summary: Select elves and omphaazes. Avoid pixies. If you decide for other races then it does not matter which races you select. If you will see some difference between races at all (except elves and omphaazes) then you will see it only in the beginning of the game.