I would say there is a difference, because they're not mutually exclusive - one is a wide scale, the other is more binary.
Being effective is simpler to determine objectively - either you can contribute to the game and the party's success, or you can't. If you have a role/job/specialty and you are capable of fulfilling it, you're effective, regardless of your party members. Someone else can be more effective than you, but that only makes you subjectively less effective, which can be fixed by out-of-game Diplomacy.
Being optimized, on the other hand, is stickier, because it can be so varied. The act of 'optimizing', at its most basic level, is simply not making bad choices. A Fighter who puts his highest stat in Strength is optimizing, as is one who chooses Power Attack. A Fighter with Power Attack and Shocktrooper is optimizing more, as is one who dips Barbarian for Pounce. It's very, very difficult to be un-optimized, and generally is either the effect of someone who's never played a system RPG before and makes a character completely unassisted, or someone with a chip on their shoulder about 'RP' who deliberately makes poor chargen decisions.
The problem comes when your character is either over-optimized or under-optimized for your group and the campaign/DM. A group of low-op players...the Sword-and-board fighter, kung-fu Monk, healbot Cleric, and fireball-slinging Sorcerer...can get along great without problems, if the DM scales challenges appropriately for what they can accomplish. Likewise, a Druid, Wizard/Archmage, DMM battle-Cleric, and Psion can co-exist in mutual harmony; their damage output and ability to solve problems in nonconventional ways is exponentially higher than the first group, but a DM prepared for such can plan ahead and still offer effective challenges, while letting everyone cut loose. The issues, and many people's prejudices against certain classes/playstyles, comes when you start mixing between them. Stick the Fighter and the battle-Cleric in the same group, and the poor Fighter will find himself rendered irrelevant by the caster who's buffed to the gills 24/7 and can still heal/contribute utility magic. The Sorcerer may have fun dropping Fireballs on enemies' heads, but when he does so only to have the Wizard fire off a Chained Split Maximized Enervation and oneshot the boss and half of his minions, there's a problem. If you put the Psion in front of a DM who's used to a Fireball Sorcerer, the simple ability of the former to throw a fireball/iceball/acidball/soundball when he so chooses can overwhelm the poor unprepared DM, and usually causes kneejerk bannings. The much-debated Tome of Battle classes are unquestionably better than the PHB melee classes they are analogues of...to groups/DMs who consider Fighters and Monks to be balanced out-of-the-box, the flexibility and damage output of Warblades and Swordsages makes them completely OP; groups that view 1d8+Str/turn and 'Flurry of Misses' as endless frustrations cry tears of happiness at being able to deal relevant damage while moving more than 5ft./turn.
This isn't always true, but when your character is seemingly without flaws because of the build, that it hard not to play or let get to your head.
I'm amused here by what I suspect is unintentional irony, because actual mechanical Flaws are generally viewed as powergaming, even by practiced optimizers.