All right, I've briefly run the gutterkin through a small adventure and a number of low-level combats to play-test them. They certainly weren't over-powered, and my play-testers said that they didn't seem weaker than the other characters, either (or perhaps my play-testers were just being nice...).
Anyway, these are the racial traits we went with:
Gutterkin Racial Traits (Version 1.3)
• +2 Dexterity, -2 Intelligence. Gutterkin are quick and strong for their size, but don't do well when in comes to thinking ahead, or thinking in abstracts, or thinking at all.
• Small: As a Small creature, a gutterkin gains a +1 size bonus to Armor Class, a +1 size bonus on attack rolls, and a +4 size bonus on Hide checks, but he uses smaller weapons than humans use, and his lifting and carrying limits are three-quarters of those of a Medium character.
• A gutterkin's base speed is 30 feet. Gutterkins' speed has helped them get out of danger on more than one occasion.
• They Bounce!: Gutterkin may stand up from prone as a free action.
• +2 racial bonus on Spot and Listen checks. Having been forced to live in particularly hazardous areas, gutterkin have learned to always be wary of potential hazards.
• +2 racial bonus on grapple checks, which increases to a +4 racial bonus when a gutterkin tries to escape a grapple. Gutterkin are scrappy, pugnacious, and hard to hold on to if they don't want to be held.
• +1 racial bonus on all saving throws. Survival of the fittest is the name of the game for gutterkin, and those that are fittest are the ones best able to shrug off the poisons, diseases, falling rubble, collapsing shanties, and other accidents that plague gutterkin communities.
• Automatic Languages: Common, Gutterkin.
• Bonus Languages: Dwarven, Elven, Orc.
• Favored Class: Ranger. A multiclass gutterkin’s ranger class does not count when determining whether he or she takes an experience point penalty for multiclassing.
Wait, there's more! We've had a lot of good ideas for racial trait variants, so I went ahead and wrote up tuffkin, the first gutterkin subrace!
Tuffkin Racial Traits
• +2 Dexterity, -2 Intelligence. Tuffkin are quick and strong for their size, but don't do well when in comes to thinking ahead, or thinking in abstracts, or thinking at all.
• Small: As a Small creature, a tutterkin gains a +1 size bonus to Armor Class, a +1 size bonus on attack rolls, and a +4 size bonus on Hide checks, but he uses smaller weapons than humans use, and his lifting and carrying limits are three-quarters of those of a Medium character.
• A tuffkin's base speed is 30 feet. Tuffkins' speed has helped them get out of danger on more than one occasion.
• Wiry Build: A tuffkin is considered to be medium sized when opposing any roll that gives a penalty to a small creature. The opposing roll must be in response to the action of another creature. For example, when making an opposed roll to resist a grapple, the tuffkin is considered to be medium sized. When attempting to grapple a foe, the tuffkin is considered to be small size.
• +2 racial bonus on Spot and Listen checks. Having been forced to live in particularly hazardous areas, tuffkin have learned to always be wary of potential hazards.
• +2 racial bonus on saving throws against poison and disease. Though not quite as lucky as gutterkin, tuffkin are noted for being much resistant to toxins and illness.
• Automatic Languages: Common, Gutterkin.
• Bonus Languages: Dwarven, Elven, Orc.
• Favored Class: Ranger. A multiclass tuffkin’s ranger class does not count when determining whether he or she takes an experience point penalty for multiclassing.
There it is. Thanks to everyone who has chimed in with comments and ideas!