In an relatively high abstract sense one might say Aikido is effective, because you learn to refine aspects that are helpful in a fight. But more concrete, or technical level, the techniques in Aikido make no sense in a fight. Why throw someone? You just let someone escape to attack you again. One could then say Aikido is not effective at all, almost useless....
All this fuels a lot of discussions. Know what you are looking for.
In my opinion effectiveness depends on one's level of ability and of course technique developed by constant practice is the only way to be effective on life and death situations.Techniques that neutralize the attacker imobilizing him are very effective and also projections or throws are very effective,depending on the situation.Throwing someone in a real fight could mean deliberately throwing him through a window,against a wall or "crash landing" him on concrete!Of course you can't practice that on a concrete...tatami or try to throw your uke through the dojo's window for obvious reasons.That doesn't make it less effective in a real fight.You can train realistically and still be inside the safety limits,that's why we learn breakfalls anyway.And once in a while you can try some surprise attacks to test your level.The attacks are real even if the knife is wooden...Let's not forget that aikido is a martial art so it should be practiced as one!