What item bonuses apply to my follower?
There are a lot of different side effects an item can have, and I assume that things like magic find have no influence on any of "our" found items at all.
However, I'm not sure about other things. For example:
- Do followers get life-steal on weapons, too?
- Does increased orb healing make any difference?
- What about +experience after kills? Will my follower level up faster?
and probably a lot more.
Is there some general rule as to what effects of an item apply to followers, and which don't?
Item perks like movement speed or life steal are individual and not shared with your party or follower. Class skills, on the other hand, can imbue party members and your follower.
You get 20% of your follower's added Magic Find, Gold Find, and XP bonuses.1 You followers don't have drops and only add to your stats.
You get none of your follower's resource bonuses, and Strength, Dexterity, and Intelligence perks increase damage for the Templar, Scoundrel, and Enchantress, respectively.2 +Vitality gear adds 10 follower HP for each point.
This is only a partial answer, but it does address one of your points. Blizzard has posted that you get 20% of some of the bonuses of your followers:
You get 20% of your follower’s Magic Find, Gold Find, and + to XP.
Source: http://www.diablofans.com/blizz-tracker/topic/218401-follower-gold-magic-find-equipment/
As a more generic method to determine which stats are affected: Open the follower's Details page as well as your own, and unequip whatever is already in the slot to test beforehand. Then equip the weapon/armor/jewelry, and see if the corresponding stat increases.
This way, you can easily check that some categories get a 20% contribution (magic find etc.) while others are unaffected.