i believe for every time you successfully get into someone's house, you get nails based on the formula [sqrt(robbing lvl)/2].  so for robbing lvl 4, you start getting 1 nail every time you get in someone's house.  for robbing lvl 16, you get 2.  for lvl 36, you'd get 3.  for lvl 64, you get 4 nails... etc.  only thing is, you'll rarely get into people's houses til at least 30 or 40 or 50 robbing lvl's.

but even when you do start getting into houses, it doesn't happen often.  those few robs will be nice (because you'll get a number of nails, plus the other goods... like the 9 rations you took from my guy earlier :p).  but the rest of the robs (from npc's ... non-player characters... aka dummy-houses), i believe you will always get either 0 or 1 nail for each successful npc rob.  hope that answers your question.

--jason

SO i assume that as your robbing lvl goes higher the beeter the chance that you will get in to a real persons house.

Nope.  Robbing level is only for how many items you get, and maybe the quality of the items.  Your stats determine if you get in ;)

-Prince K

but pretty much for your robbing lvl to go higher, you have to level up a number of times along the line.  and then you have more atty points to distribute.  which means you have a better chance of getting into some places.  so there is some correlation, just not direct.
--jason