My thoughts:
1) Jiyeon or not, the person/people who retained/proliferated this video should be punished. Who knows, it may have been a young boy on the other side of the chat, which would be less creepy, but it also could have been some sick older dude manipulating a minor, and the video is contraband in any case.
2) I'm mad at whoever is spreading it around, especially with attachments trying to prove it is Jiyeon. If it is her, it is her past, why crush her life now? Moreover, if Jiyeon is hurt then T-ara as a whole is hurt, and the other girls have absolutely nothing to do with it. What is with these people and destroying the lives of others?
3) I'm not 100% convinced to either side. Initially it seems quite convincing, but then people have pointed out the different handedness, door direction, phone, piano, wall trim, lighting, extrapolated room size, etc. It is enough for me to swing back and strongly doubt. However, if it is not her then it is the most elaborate and vicious hoax I have ever seen. I would be interested in an analysis of the video encoding and file dates of the different videos, which are embedded in them.
4) I hope the other girls believe and trust her, or if there is anything to come clean about, that it happens at least between them if not with the public at large, so they can be united. It would be terrible for something like this to cause a lack of trust between them. Fact of the matter is that everyone is curious and experiments in order to learn these parts of life at some time. If they are on the internet, it is likely to happen sooner. I wouldn't bat an eye at nearly anything confessed, even from my beloved Hyomin, who is actually pretty open about her interest in sexual things. So I hope they can support her fully.
5) Lies told enough times start to stick. The rate of people who think Obama is a Muslim continues to rise because of on stupid rumor that has been thoroughly debunked time and again. So please, let's forget this and move on and hopefully let T-ara have smooth promotions as soon as possible.