Saw this last night...*spoilers*
I thought this film was not all that great, and the really annoying part was that I saw many ways in which it could have been better.
First of all, the back of the DVD box explained that Thomas had a platonic relationship with Cathy, and that he was falling in love with her. I did not see this at all. If I hadn't read that, I would have assumed that it was indeed a sexual thing for him, and that he was lying to the cops when he said it wasn't. Also, I wasn't sure if he was able to view the website for free somehow, or if he really was paying to talk to her in a platonic way. I was very intrigued by this aspect of the story, but they didn't seem to want to delve into Thomas's character enough. Claire even asked him how he met Cathy, and he didn't give her a straight answer.
Also, in the beginning, it seemed as though they were trying to portray Thomas as lonely and painfully shy. Then, halfway through the film, he's got 2 beautiful women throwing themselves at him out of no where. I'm not saying this can't happen. I understood the motivation of both women for being attracted to him. But he seemed to handle it a little too smoothly. All of a sudden, he's no longer socially maladjusted. I thought Edward Furlong did a good job, despite the inconsistencies in the script.