ToME Wiki
General Info
The Sneakiness skill boosts your character's searching and perception abilities. This means finding secret doors, traps, and trapped chests. There isn't a real reason to pump this on any character build I can think of, but I wanted to include this page for completeness.
Another thing to remember is that "Tactics" and "Explore" also affect searching/perception.
Code-Related Information
Sneakiness modifes your ability to Searching and Perception. Specifically searching is your Skill level in Sneakiness times .7+5. So the scale (not counting equipment) would be searching of 5 at skill level 0 to 40 at skill level 50. Perception is your Skill level in Sneakiness times .5+5. So the scale (not counting equipment) would be searching of 5 at skill level 0 to 30 at skill level 50. The exacts of this I got courtesy of Killerbunnies.