This thread is being made for Kyeruu. I will not flame and I will not name-call. I will post things from their ideology that I remember to the best of my ability. I will also post a little bit about translations. This will be short, mind you, so please bear with me. I am rusty in terms of other religions since I'm no longer a Catholic apologist, so I will point out if I don't remember something clearly and you are more than welcome to correct me.
First thing I'd like to bring up: The creation of the Jehovah's Witnesses. The JWs were originally created by a man named Charles Taze Russell. He was originally a Presbyterian, but joined the Seventh Day Adventists when he went back to religion, leading many Bible studies. Eventually he split from them with his own ideas and would later go on to found his own group, the Zion's Watchtower Bible and Tract Society. Later on he'd go on to reinterpret the Bible, following closely to the Catholic version of the Bible with is own additions and revisions. He eventually died in 1916. His position was taken over by "Judge" Joseph Franklin Rutherford (the "Judge" bit given to him by people because of his background in Law). Eventually under Rutherford's reign as president there'd be a split and the group loyal to him would reform themselves as the Jehovah's Witnesses (circa 1931). Personal points I'd like to bring up was that many saw Russell as a con artist and were distrustful of him and how he would handle things with the Zion's Watchtower Bible and Tract Society.
Next thing I want to bring up is translation: Russell claimed to be able to translate ancient Greek, Latin, and Hebrew. In reality all he did was take the Bible and make some changes and additions and revisions as he saw fit, but even to this very day the JWs will claim that he was able to truly translate things the way they are written. The biggest mistake they make is in the Greek word "logos," which means "the word." I can't recall everything about how it's mistranslated and defended, but they take it to be multiple "words."
Prophecies: Russell predicted there'd be a cataclysmic and celestial war in 1914 that would signify the end of the world. After waiting for the end to occur in that time, it never did, so they had to change their story and continually change the end time date.
Other miscellaneous things I'd like to bring up: They believe that Jesus and Satan are actually brothers. They deny the Trinity, a belief held dear by much of mainstream Christianity. As for salvation, well, they believe only 144,000 will truly be allowed into heaven and as far as that goes, the first 144,000 would technically already have been saved and in heaven now.
For other things, I can only refer you to these sites:
http://www.rapidnet.com/~jbeard/bdm/Cults/jw.htm and
http://www.apologeticsindex.org/j02.html
It's better informed and has more information than I have. I'm quite rusty in my knowledge of the JWs, but I hope this was still a bit interesting and informing.
As for my personal opinion of them (since this is Debate AND Opinion): I simply believe they are a cult. They don't allow blood transfusions, regardless of the consequences and circumstances, they hold far-out beliefs as far as Trinity and Jesus goes, and they are very cruel with their disfellowshipping.