These three areas sound like good deals. I'm a huge fan of knife fighting styles (just all Hellhound, I'm still bugging him about EN Arsenal Daggers), and I like feats that let you do more. The multi-class options sound intersting too. Unlike most here, I liked the fact that the Illumians were included in Races of Destiny because they'e a race that specializes in mutli-classing. I'm hoping for some good synergy between the Complete Adventurer and Races of Destiny.
I am worried about an 'extensive' feat selection though, and it sounds like there are going to be a lot of PrCs, which is the opposite direction taken with Divine and Arcane.
9. Focus in with Feats: Complete Adventurer's extensive feats section offers plenty of options for sharpening and focusing your character's abilities. For example, the Extraordinary Spell Aim feat allows a spellcaster to shape an area spell so that its effects flow around a selected creature. Now your character can blast away with spells and not worry about harming an ally!
8. Expanded Multiclassing Options: Many of the new feats in Complete Adventurer help to make some often-overlooked multiclassing options more viable. For example, how about a singing paladin? The Devoted Performer feat lets a character stack paladin and bard levels together to determine damage for the smite evil ability as well as uses per day of bardic music.
7. Go for Some Prestige: If your character takes care of business in a special way, these new prestige classes are for you. For example, the daggerspell mage and daggerspell shaper combine arcane magic, dagger fighting, and wildshape. The bloodhound excels at tracking down elusive foes, and the ghost-faced killer can bring fear and silent death to his enemies.