Our house rules are basically split into three parts:

1) Winds of Magic- a conversion that is mostly a compilation of Random Mutation tables and translating 2e's rules on Chaos Manifestations for 1e Magic system

2) Different Ways. Point - buy system for Warhammer (since well, a lot of people complain about having to roll stats), as well as the more DnD 3.0 method for rolling the characteristics. Also a few pages of traits, that can be bought with points, or bought to gain some points - mostly to solve a problem that an ugly hag who completed Demagogue profession would have a much easier time seducing an adventurer then even the most beautiful of women, whom is a starting character in WFRP (and therefore has max 40 Fellowship, if human).

3) Weapons & Combat Master - probably the core of house rules. Revision of armour systems (You can have up to 4 armour points, but well - that 4th point is actually a very bad idea ), a lot of various hand weapons added, most just for flavour - People who made those rules were mostly medieval weapons and combat enthusiast, so they both cared about getting combat even more gritty, as well as more flavourful by introducing a rich set of weapons for even those GMs like me, who don't know that much about medieval weaponry, to use. Also making the ranged weaponry much, much more powerful - especially gunpowder weaponry and crossbows. The actual fighting changes mostly cover damage to armour, damage to unprotected targets, and a few fight "moves" - basically, if your character has certain skills from 1e, he can use special attacks. For example, if you have a Strong Blow, your character knows how to utilise efficiently an attack from the wrist (sorry, this is a rough translation) - you attack quicker and more accurately, but you deal less damage.

There are no specific rules for world - which is fine. My friend likes to run a down - to - the - earth Warhammer, where we mostly focus on small victories, while I like to span plots of really big grandeur, and throw my PCs into them Hitchcock style, aka "heroes from accident" - and that's what those house rules allow me. The combat is still gritty, but the party can survive a bit more if they care for their armour, and if they learn how to use ranged weaponry to their advantage.

And what are your houserules for Warhammer, especially if you keep on rocking the old dog of 1e?