Here's what I posted on the WotC boards about the class:
I don't think the various focuses are all that balanced with each other.
Arcane Focus and Divine Focus blow the other focuses out of the water. Even a 1st level Chameleon gets a decent amount of spells (as long as their spellcasting stat is 14+), and many of those spells can duplicate the effects gained from the other focuses. By 5th level, you can throw a fireball for 10d6*, or have enough healing to take care of the average adventuring party for the day.
Combat Focus is pretty good. +2 to hit and damage is quite useful, and +4 is even better. Best used when you're going through a long adventure where you would burn through spells too quickly. Combined with the medium BAB you'll do okay faking the fighter role...though the lack of feats is a definate problem.
Stealth Focus is pretty lame. Arcane Focus can make you a passable wizard, Divine Focus can make you a passable cleric or druid, Combat Focus can make you a passable fighter, but Stealth Focus won't make you a passable rogue - the +2 bonus is minimal, and even +4 isn't going to help unless you already have several ranks in the skill. You're better off shelling out some gold for magic items that give you much better bonuses at a reasonable price. +2 on Disable Device and Open Lock is the same as buying masterwork thieves' tools.
Wild Focus is worse than Stealth Focus - you don't even get the Track feat out of it. Unless you're about to be eaten by a bear, don't bother.
Overall, I think a few levels of Chameleon are a great way to turn a rogue into a true jack of all trades, but the only way I'd take 10 levels in the class is if I wanted to milk the double class level feature for spellcasting. A Rogue 5/Chameleon 10 can throw chain lightning at 20d6 on the primary, and 10d6 on up to 20 other targets - that's tougher than the same spell from a 15th level wizard.
* This means a Rogue 5/Chameleon 5 throws a fireball as powerful as one thrown by an equal-level wizard. Caster level equaling double class level is really unbalanced, as my chain lightning example shows. Expect this to be the subject of errata shortly after release.