Towards the end when Will urges Scott to tell the truth, you can see the emblem of the well known "SpeeDee Oil Change" in the background (close to the ceiling) In the story the shop is supposed to be "Blakelee Brakes," which was said to be a franchise.
When Will comes to Ronnie's house to apologize, there is a sweat stain on the front of his shirt. Ronnie slams the door in Will's face but when Steve opens up the door again the stain is no longer on Will's shirt.
When Will and Ronnie are arguing on the beach about her not wanting to be another in his long line of girls she is wearing a necklace. At one point she turns to leave and when she turns back around the necklace is tucked into the neckline of her shirt. Once again she turns to leave and when she turns back the necklace is back on the outside of her shirt.
The film takes place on Tybee Island, GA (as indicated by the Tybee Island Baptist Church sign) and yet Will volunteers at and takes Ronnie to the Georgia Aquarium which is actually located 260 miles away in Atlanta.
Closeups of Ronnie's hands as she plays the piano for the first time clearly show a large wart or mole on the back of her right hand. But you can see that Miley Cyrus has no such blemish on her right hand.