sure, all the time. but like niky said, it has to have good logic and credible facts to back it up. there's a lot i don't know about a lot of topics, so i learn from a lot of threads and i always end up changing my opinion if i don't know much about the topic to begin with.

i also consider the source. i tend to take people who usually present their stuff intelligently at their word, and discount people who i have seen post really stupid things.