Very true - spending time with the person is key.
That said, I think the thing that perplexes others is that I require time to myself to think about things - ponder my feelings, think about the other person, where I see the relationship going, etc etc. Basically people don't get it that I need time to let things sift through my brain. So this might mean not seeing the other person as much as the other person would like, or as often. And that can make for some tricky/awkward conversations. I want to clarify though that this tends to be just in the early stages of dating. Once I'm in a relationship, it starts to become a non-issue.
In early stages, I don't do spontaneity terribly well, and it can be hard for me to just 'let go' and roll with it and just see where the relationship goes of its own accord -- it boils down to the fact that I take these things seriously, so it can be hard for me to just have 'fun' with a person when my mind automatically projects far into the future. I do it in spurts, but in the end I always need to fall back into my internal world to assess everything and really take a step back and, well, analyze the relationship. Basically, I require that - I might be able to push it back for a while, but I always end up having to go there. So it's that needed alone time - which would be pulling the reins, I suppose - that I think people find confusing. And perhaps understandably so.