You can write in information even if you don't pay ... in the weather section. But you do get to do a lot more if you pay.
One of the differences between logging information on bikejournal, and logging information here on BF is that on bikejournal, distances get added up automatically for you. And it will tell you how many rides you've done in a month or year. And you can see how you're doing compared with other people.
I'm sort of hovering around the 1300-1500 area right now.