Thinking it over further, I am posting my Acrobat class here. Feel free to pick this apart or make suggestions. The question is: Would you want to play this class, or could you see someone wanting to?
Edit: I can't seem to format this right at all. I think I'll throw it on google docs, but that will have to wait until I get home.
Hit Dice: d6 per level up to 9th level. After 9th level, acrobats receive 2 hit points per level
Races Permitted: Any (as thief)
Weapons Permitted: Hand axe, bo stick, caltrop, club, dagger, garrot, jo stick, knife, lasso, sap, scimitar, spear, quarter staff, long sword, short sword, whip, blowgun, short bow, hand crossbow, light crossbow, javelin, sling, staff sling, dart, poison (if evil), flaming oil
Armor Permitted: Leather (not studded) only, no shield
Requirements: Str 15, Dex 16. An acrobat with both strength and dex higher than 16 earns 10% bonus experience. Both strength and dexterity are considered prime requisites for the acrobat.
Acrobats may be of any alignment, though many, through their associations with thieves, tend toward neutrality or even evil. Few acrobats are lawful.
Acrobats have the following special abilities:
-Tightrope walking, Pole Vaulting, High Jump, Standing/Running Broad Jump, Tumble Evasion, Tumble Falling as described in Unearthed Arcana.
-Thief skills: An acrobat may climb walls and move silently as a thief of the same experience level. An acrobat may also pick pockets and hear noise as a thief three levels lower.
-Acrobats are accomplished in the art of throwing. They receive a bonus to hit of +1 per five experience levels on all attacks made with thrown or hurled weapons. In addition, at the fourth level, an acrobat may specialize in one particular type of thrown weapon as if he were a fighter. The specialization benefits supercede the to hit bonus for that particular weapon. At 8th level, the acrobat may specialize in a second thrown or hurled weapon, or may double specialize in the weapon taken at 4th level. Note that the acrobat is still required to spend the necessary proficiency slots to specialize or double specialize.
-Tumble Attack: An acrobat's combat style is very fluid and often confounding to an opponent. Every round that an acrobat engages an opponent in melee, he may make one of his attacks a tumble attack. In addition to the normal to-hit chance, there is a percentage chance that the acrobat will force the opponent into a compromising situation. An opponent so affected receives no bonus from Dexterity or Shield on their next action, all attacks made are at a -2 penalty, and if they move more than one half their movement rate, they must save vs. petrification or fall prone. Note that the percentage is rolled even if the acrobat's original attack misses. The acrobat can fluster only one such opponent per round, and opponents who are non-intelligent, constructs, or undead are generally not effected. On a natural 20, the percentage is doubled in addition to any beneficial effects of a 20 your DM may have devised.
-Tumbling Movement: An acrobat is trained at quickly traversing adverse terrain by jumping, handspringing, and otherwise clearing obstacles. Starting at 3rd level, adverse terrain only affects an acrobat one category worse then normal. (For instance, terrain that allows only 1/2 movement would allow the acrobat 3/4 movement, while terrain that allows 3/4 movement would not hinder the acrobat at all) At 9th level, this improves two steps, such that terrain that would normally slow a character by half does not hinder the acrobat, and even terrain that would normally slow a character to 1/4 will allow the acrobat to move up to 3/4 normal speed.
The ability tables and experience table for the Acrobat follow (I apologize for the ugly format, but it's just a rough draft.) The tables regarding armor, race, strength, and dex from Unearthed Arcana all apply to the acrobat.
Edit: The acrobat's tables can be found here: Acrobat!