Yes! I'm exactly this way. It often takes a while for me to think of what it is I want to say...to gather the words and form things in my mind. Sometimes I'll be talking with someone and not have a lot to say about a topic, but then think about it, come up with something and bring the topic up again a few days later. I just needed the time to figure out what I really think. I'll sometimes warn new friends that I'm this way just so they won't think I'm stupid or incompetent. It just takes a little time for me to sort through my thoughts.
Yeah, so definitely keep this in mind about ISFp's. I can tell you that I really do appreciate it when people are patient with me. I think ISFp's may be the sort that people listen to when they have something to say because they don't say much, but when they do they've given it a lot of thought, so it should be good. Really, ISFp's aren't stupid...we just need time to think things through before answering...especially if it's a controversial topic, we don't want to offend.