Just a short post on conversations in SWTOR, and the consequences of choosing one reply over the other:
What many blogs have already reported is that sometimes replies in conversations can give you light side or dark side points. By default a symbol in the middle of the wheel where you click to choose those options shows whether your reply gives light side points, dark side points, or nothing. You can turn that off if you prefer to be surprised, although in many cases it is rather obvious which reply is good or bad.
Sometimes conversation options are marked with a consequence in brackets, like [Attack] or [Refuse quest]. Unsurprisingly that means exactly what it says on the label, so choosing the option with the [Attack] label leads to you getting into a fight.
In the early levels, most of the time your conversation choices are completely irrelevant. You can test that by either choosing [Refuse quest] at the end of a conversation, or pressing ESC, both of which options make the NPC completely forget you, so you can start the same conversation again and choose other options. And it turns out that whether you tell the crazy Sith Lord that his animal dissection experiments are crazy or whether you admire him for them has no consequences. It only slightly alters the way he responds, but then leads to exactly the same next bit of conversation and reply options.
Once you get a companion around level 9, reply options have another angle added: They change the affection level of your companion. You can look up what your companion likes and dislikes in the codex. And when for example it says that your companion likes protecting women, and dislikes hurting them (even the bad ones), your choice of action in the next conversation with that girl who betrayed you will change your companions affection level towards you. Even if otherwise there is no consequence, nor light/dark side points attached to those options. Note that there is no hint telling you about that, you need to be attentive to your companion's likes and dislikes without the game helping you.