A couple things that will always strike me in OOTP that definitely prove that Hermione likes Harry in more than just a platonic way is the way she acted whenever finding out about Harry and Cho's first kiss. She acted distant, and extremely dull. Not at all happy for her friend in the least. And also the infamous frown on her face when initially finding out. What did Ron have.. Mingled curiosity and What did Hermione have? A FROWN. Look at the comparsion of reactions from Ron and Hermione. Ron is jumping up and down and is genuinely excited for Harry while Hermione is distant, off in her own world, with an instant frown on her face when first learning about the kiss. JK certainly did not need to include that frown on Hermione's face. She MEANT for Hermione to be frowing and she meant to show the differences in reactions from Ron and Hermione during this. VERY TELLING.
The other thing that strikes me is how Hermione conveniently planned a meeting with Harry during his date with Cho. On Valentine's Day on top of it all.
I mean, Hermione could not have waited until Harry and Cho's date was over later that evening or even planned the meeting the following day. Nope, HAD to be DURING the date. Hee.
Cho's jealousy of Hermione is also key. In fact, the pattern that JK used in GOF with Krum being jealous of Harry and Hermione and then in OOTP, it is Cho's turn of being jealous of Harry and Hermione. Isn't that pattern mighty convenient?
I think JK is trying to make a point, don't you?