The up side to a "watch topic", is that you will for sure see the conversation, but it will take longer.
On the other hand, a "quote" feature will only work if the person tags you. (i can write
@ernie15 If a "watch topic" feature is implemented/quote] or without the "@ernie15")
and the up side is that you can see the comment right away.
I think that the best idea is that when a person qoutes someone, the site will automatically ask who you are qouting it from.