Let's see.
In early to mid Part I, Sakura was a Sasuke fangirl. She was weak, immature, and had a one-track mind. Yes, she had her good moments, but for the most part, spent all of her time obsessing over Sasuke.
When Sakura was obsessed over Sasuke, she was a terrible kunoichi. All that was on her mind was "Sasuke Sasuke Sasuke." So she never really had time to improve herself.
After Sasuke left, there was a period of time where Sakura just didn't know what to do with herself. I daresay if it wasn't for Naruto's pep talk, she would have just come to a stand still.
She became a ninja because of Sasuke, but grew as a ninja because of Naruto. She saw that Naruto was willing to forge ahead even though he'd suffered more than her. That's when she decided that she was really going to do something. Right after Naruto's speech, she took a chance and went bravely up to Tsunade asking her to take her on as her apprentice. Keep in mind that Sakura barely knew Tsunade and that Tsunade must have intimidated her in one way or another. But she asked anyways with no hesitation.
That, to me, says a lot. When Sakura was hung up on Sasuke, she did nothing and didn't improve at all. But after Sasuke left, and with Naruto's help, she got the boost she needed. In my opinion, her transition from Sasuke to Naruto made her stronger.
If she had stayed a Sasuke fangirl and a Naruto hater, she'd be no where, that's for sure. So, yes, falling in love with Naruto is a very underestimated part of her development. Though I'm not saying everything she does relies on Naruto. No, he only gave her the determination to do it. She got the old Talk no Jutsu from Naruto and it's thanks to him that she is where she is now as a kunoichi.
Also, I'd like to point out that her feelings for Sasuke did mature, but only in the sense that she went beyond the fangirling and hero worship to actual genuine concern. I don't think her love for Sasuke grew stronger though. I think it actually transitioned from love (or at least insane fangirlism) to concern and concern only. It all started after Sasuke got his curse mark. From that point on, she ceased her worship, and her love ceased along with it. Not once do I recall her admiring Sasuke. Now she's just worried.
It's opposite for Naruto, though. It went from annoyance and resentment to concern AND love. With them, there was room for improvement, and that's exactly what happened.
Edited by Froot, 22 February 2010 - 10:50 PM.